Method and apparatus for image encoding and decoding using temporal motion information

ABSTRACT

Disclosed herein are a decoding method and apparatus and an encoding method and apparatus that perform inter-prediction using a motion vector predictor. For a candidate block in a col picture, a scaled motion vector is generated based on a motion vector of the candidate block. When the scaled motion vector indicates a target block, a motion vector predictor of the target block is generated based on the motion vector of the candidate block. The motion vector predictor is used to derive the motion vector of the target block in a specific inter-prediction mode such as a merge mode and an AMVP mode.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. application Ser. No. 16/964,878, filed on Jul. 24, 2020, which was the National Stage of International Application No. PCT/KR2019/001096 filed on Jan. 15, 2019, which claims priority to Korean Patent Applications: KR10-2018-0010177, filed on Jan. 26, 2018, and KR10-2019-0009837, filed on Jan. 25, 2019, with the Korean Intellectual Property Office, which are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The following embodiments relate generally to a video decoding method and apparatus and a video encoding method and apparatus, and more particularly, to an image decoding method and apparatus and an image encoding method and apparatus that use temporal motion information.

BACKGROUND ART

With the continuous development of the information and communication industries, broadcasting services supporting High-Definition (HD) resolution have been popularized all over the world. Through this popularization, a large number of users have become accustomed to high-resolution and high-definition images and/or videos.

To satisfy users' demand for high definition, many institutions have accelerated the development of next-generation imaging devices. Users' interest in UHD TVs, having resolution that is more than four times as high as that of Full HD (FHD) TVs, as well as High-Definition TVs (HDTV) and FHD TVs, has increased. As interest therein has increased, image encoding/decoding technology for images having higher resolution and higher definition is continually required.

An image encoding/decoding apparatus and method may use inter-prediction technology, intra-prediction technology, entropy-coding technology, etc. so as to perform encoding/decoding on a high-resolution and high-definition image. Inter-prediction technology may be technology for predicting the value of a pixel included in a target picture using temporally previous pictures and/or temporally subsequent pictures. Intra-prediction technology may be technology for predicting the value of a pixel included in a target picture using information about pixels in the target picture. Entropy-coding technology may be technology for assigning short code words to frequently occurring symbols and assigning long code words to rarely occurring symbols.

Various inter-prediction technologies and intra-prediction technologies have been developed for more accurate prediction.

DISCLOSURE Technical Problem

An embodiment is intended to provide an encoding apparatus and method and a decoding apparatus and method that perform inter-prediction using a motion vector predictor of a target block.

An embodiment is intended to provide an encoding apparatus and method and a decoding apparatus and method that generate a motion vector predictor of a target block using the motion vector of a candidate block in a co-located picture (col picture).

Technical Solution

In accordance with an aspect, there is provided a decoding method, including generating a motion vector predictor of a target block based on a motion vector of a candidate block in a co-located picture (col picture) for the target block; and performing inter-prediction for the target block based on the motion vector predictor.

Whether the motion vector predictor is to be generated may be determined based on an inter-prediction mode of inter-prediction information of the target block.

The motion vector predictor may be generated when the inter-prediction mode is an Advanced Motion Vector Prediction (AMVP) mode, a merge mode or a skip mode.

The motion vector predictor may be added as a candidate to a list for the target block.

Generating the motion vector predictor may include determining whether the motion information of the candidate block is to be used to generate the motion vector predictor of the target block; and generating the motion vector predictor of the target block based on the motion information of the candidate block.

A first scaled motion vector may be generated by applying first scaling to the motion vector of the candidate block.

When the first scaled motion vector indicates the target block, the motion information of the candidate block may be used to generate the motion vector predictor of the target block.

The first scaled motion vector may be generated by multiplying a first scaling coefficient by the motion vector of the candidate block.

The first scaling coefficient may be a value obtained by dividing a first temporal distance by a second temporal distance.

The first temporal distance may be a temporal distance from the col picture to a target picture.

The second temporal distance may be a temporal distance from the col picture to a reference picture for the candidate block.

The target picture may be a picture including the target block.

The first scaling coefficient may be a coefficient for scaling the motion vector of the candidate block depending on a temporal direction between a target picture and a reference picture for the target block.

The target picture may be a picture including the target block.

The motion vector predictor may be generated by applying second scaling to the motion vector of the candidate block.

The motion vector predictor may be generated by multiplying a second scaling coefficient by the motion vector of the candidate block.

The second scaling coefficient is a value obtained by dividing a third temporal distance by a second temporal distance.

The third temporal distance may be a temporal distance from a target picture to a reference picture for the target block.

The second temporal distance may be a temporal distance from the col picture to a reference picture for the candidate block.

The target picture may be a picture including the target block.

The candidate block may include multiple candidate blocks.

An average value of multiple motion vectors of the multiple candidate blocks may be used to generate the motion vector predictor.

One or more motion vectors may be selected from among multiple motion vectors of the multiple candidate blocks based on inter-prediction indicators of the multiple candidate blocks or an inter-prediction indicator of the target block.

The selected one or more motion vectors may be used to generate the motion vector predictor.

One or more motion vectors may be selected from among multiple motion vectors of the multiple candidate blocks based on reference picture indices of the multiple candidate blocks or a reference picture index of the target block.

The selected one or more motion vectors may be used to generate the motion vector predictor.

One or more motion vectors may be selected from among multiple motion vectors of the multiple candidate blocks based on at least one of coding parameters of the target block.

The selected one or more motion vectors may be used to generate the motion vector predictor.

Whether the motion vector of the candidate block is to be used to generate the motion vector predictor may be determined based on a magnitude of a motion vector related to the candidate block.

Whether the motion vector of the candidate block is to be used to generate the motion vector predictor may be determined based on a size of the target block.

In accordance with another aspect, there is provided an encoding method, including generating a motion vector predictor of a target block based on a motion vector of a candidate block in a co-located picture (col picture) for the target block; and performing inter-prediction for the target block based on the motion vector predictor.

In accordance with a further aspect, there is provided a method for generating a motion vector predictor, including determining whether motion information of a target block is to be used to generate a motion vector predictor of the target block; and generating the motion vector predictor of the target block based on the motion information of the candidate block.

Advantageous Effects

There are provided an encoding apparatus and method and a decoding apparatus and method that perform inter-prediction using a motion vector predictor of a target block.

There are provided an encoding apparatus and method and a decoding apparatus and method that generate a motion vector predictor of a target block using the motion vector of a candidate block in a col picture.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating the configuration of an embodiment of an encoding apparatus to which the present disclosure is applied;

FIG. 2 is a block diagram illustrating the configuration of an embodiment of a decoding apparatus to which the present disclosure is applied;

FIG. 3 is a diagram schematically illustrating the partition structure of an image when the image is encoded and decoded;

FIG. 4 is a diagram illustrating the form of a Prediction Unit (PU) that a Coding Unit (CU) can include;

FIG. 5 is a diagram illustrating the form of a Transform Unit (TU) that can be included in a CU;

FIG. 6 illustrates splitting of a block according to an example;

FIG. 7 is a diagram for explaining an embodiment of an intra-prediction procedure;

FIG. 8 is a diagram for explaining the locations of reference samples used in an intra-prediction procedure;

FIG. 9 is a diagram for explaining an embodiment of an inter-prediction procedure;

FIG. 10 illustrates spatial candidates according to an embodiment;

FIG. 11 illustrates the order of addition of motion information of spatial candidates to a merge list according to an embodiment;

FIG. 12 illustrates a transform and quantization process according to an example;

FIG. 13 illustrates diagonal scanning according to an example;

FIG. 14 illustrates horizontal scanning according to an example;

FIG. 15 illustrates vertical scanning according to an example;

FIG. 16 is a configuration diagram of an encoding apparatus according to an embodiment;

FIG. 17 is a configuration diagram of a decoding apparatus according to an embodiment;

FIG. 18 illustrates a col block in a col picture according to an example;

FIG. 19 illustrates a TMVP acquisition process according to an example;

FIG. 20 illustrates a TMVP acquisition process and a UTMVP acquisition process according to an example;

FIG. 21 illustrates a UTMVP generation process according to an example;

FIG. 22 illustrates a UTMVP generation process according to an example;

FIG. 23 is a flowchart of an inter-prediction method performed by a decoding apparatus according to an embodiment;

FIG. 24 is a flowchart of an inter-prediction method performed by an encoding apparatus according to an embodiment;

FIG. 25 is a flowchart of a method for generating a motion vector predictor of a target block according to an embodiment;

FIG. 26 is a flowchart of a method for determining whether motion information of a candidate block is to be used to generate a motion vector predictor according to an embodiment;

FIG. 27 is a flowchart of a method for generating a motion vector predictor of a target block based on motion information of a candidate block according to an embodiment;

FIG. 28 is a flowchart of a method for generating a motion vector predictor of a destination block according to an embodiment; and

FIG. 29 is a flowchart of a method for generating a motion vector predictor of a target block using a specified condition according to an embodiment.

BEST MODE

The present invention may be variously changed, and may have various embodiments, and specific embodiments will be described in detail below with reference to the attached drawings. However, it should be understood that those embodiments are not intended to limit the present invention to specific disclosure forms, and that they include all changes, equivalents or modifications included in the spirit and scope of the present invention.

Detailed descriptions of the following exemplary embodiments will be made with reference to the attached drawings illustrating specific embodiments. These embodiments are described so that those having ordinary knowledge in the technical field to which the present disclosure pertains can easily practice the embodiments. It should be noted that the various embodiments are different from each other, but do not need to be mutually exclusive of each other. For example, specific shapes, structures, and characteristics described here may be implemented as other embodiments without departing from the spirit and scope of the embodiments in relation to an embodiment. Further, it should be understood that the locations or arrangement of individual components in each disclosed embodiment can be changed without departing from the spirit and scope of the embodiments. Therefore, the accompanying detailed description is not intended to restrict the scope of the disclosure, and the scope of the exemplary embodiments is limited only by the accompanying claims, along with equivalents thereof, as long as they are appropriately described.

In the drawings, similar reference numerals are used to designate the same or similar functions in various aspects. The shapes, sizes, etc. of components in the drawings may be exaggerated to make the description clear.

Terms such as “first” and “second” may be used to describe various components, but the components are not restricted by the terms. The terms are used only to distinguish one component from another component. For example, a first component may be named a second component without departing from the scope of the present specification. Likewise, a second component may be named a first component. The terms “and/or” may include combinations of a plurality of related described items or any of a plurality of related described items.

It will be understood that when a component is referred to as being “connected” or “coupled” to another component, the two components may be directly connected or coupled to each other, or intervening components may be present between the two components. It will be understood that when a component is referred to as being “directly connected or coupled”, no intervening components are present between the two components.

Also, components described in the embodiments are independently shown in order to indicate different characteristic functions, but this does not mean that each of the components is formed of a separate piece of hardware or software. That is, the components are arranged and included separately for convenience of description. For example, at least two of the components may be integrated into a single component. Conversely, one component may be divided into multiple components. An embodiment into which the components are integrated or an embodiment in which some components are separated is included in the scope of the present specification as long as it does not depart from the essence of the present specification.

Further, it should be noted that, in the exemplary embodiments, an expression describing that a component “comprises” a specific component means that additional components may be included within the scope of the practice or the technical spirit of exemplary embodiments, but does not preclude the presence of components other than the specific component.

The terms used in the present specification are merely used to describe specific embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless a description to the contrary is specifically pointed out in context. In the present specification, it should be understood that the terms such as “include” or “have” are merely intended to indicate that features, numbers, steps, operations, components, parts, or combinations thereof are present, and are not intended to exclude the possibility that one or more other features, numbers, steps, operations, components, parts, or combinations thereof will be present or added.

Embodiments will be described in detail below with reference to the accompanying drawings so that those having ordinary knowledge in the technical field to which the embodiments pertain can easily practice the embodiments. In the following description of the embodiments, detailed descriptions of known functions or configurations which are deemed to make the gist of the present specification obscure will be omitted. Further, the same reference numerals are used to designate the same components throughout the drawings, and repeated descriptions of the same components will be omitted.

Hereinafter, “image” may mean a single picture constituting a video, or may mean the video itself. For example, “encoding and/or decoding of an image” may mean “encoding and/or decoding of a video”, and may also mean “encoding and/or decoding of any one of images constituting the video”.

Hereinafter, the terms “video” and “motion picture” may be used to have the same meaning, and may be used interchangeably with each other.

Hereinafter, a target image may be an encoding target image, which is the target to be encoded, and/or a decoding target image, which is the target to be decoded. Further, the target image may be an input image that is input to an encoding apparatus or an input image that is input to a decoding apparatus.

Hereinafter, the terms “image”, “picture”, “frame”, and “screen” may be used to have the same meaning and may be used interchangeably with each other.

Hereinafter, a target block may be an encoding target block, i.e. the target to be encoded and/or a decoding target block, i.e. the target to be decoded. Further, the target block may be a current block, i.e. the target to be currently encoded and/or decoded. Here, the terms “target block” and “current block” may be used to have the same meaning, and may be used interchangeably with each other.

Hereinafter, the terms “block” and “unit” may be used to have the same meaning, and may be used interchangeably with each other. Alternatively, “block” may denote a specific unit.

Hereinafter, the terms “region” and “segment” may be used interchangeably with each other.

Hereinafter, a specific signal may be a signal indicating a specific block. For example, the original signal may be a signal indicating a target block. A prediction signal may be a signal indicating a prediction block. A residual signal may be a signal indicating a residual block.

In the following embodiments, specific information, data, a flag, an element, and an attribute may have their respective values. A value of “0” corresponding to each of the information, data, flag, element, and attribute may indicate a logical false or a first predefined value. In other words, the value of “0”, false, logical false, and a first predefined value may be used interchangeably with each other. A value of “1” corresponding to each of the information, data, flag, element, and attribute may indicate a logical true or a second predefined value. In other words, the value of “1”, true, logical true, and a second predefined value may be used interchangeably with each other.

When a variable such as i or j is used to indicate a row, a column, or an index, the value of i may be an integer of 0 or more or an integer of 1 or more. In other words, in the embodiments, each of a row, a column, and an index may be counted from 0 or may be counted from 1.

Below, the terms to be used in embodiments will be described.

Encoder: An encoder denotes a device for performing encoding.

Decoder: A decoder denotes a device for performing decoding.

Unit: A unit may denote the unit of image encoding and decoding. The terms “unit” and “block” may be used to have the same meaning, and may be used interchangeably with each other.

-   -   “Unit” may be an M×N array of samples. M and N may be positive         integers, respectively. The term “unit” may generally mean a         two-dimensional (2D) array of samples.     -   In the encoding and decoding of an image, “unit” may be an area         generated by the partitioning of one image. In other words,         “unit” may be a region specified in one image. A single image         may be partitioned into multiple units. Alternatively, one image         may be partitioned into sub-parts, and the unit may denote each         partitioned sub-part when encoding or decoding is performed on         the partitioned sub-part.     -   In the encoding and decoding of an image, predefined processing         may be performed on each unit depending on the type of the unit.     -   Depending on functions, the unit types may be classified into a         macro unit, a Coding Unit (CU), a Prediction Unit (PU), a         residual unit, a Transform Unit (TU), etc. Alternatively,         depending on functions, the unit may denote a block, a         macroblock, a coding tree unit, a coding tree block, a coding         unit, a coding block, a prediction unit, a prediction block, a         residual unit, a residual block, a transform unit, a transform         block, etc.     -   The term “unit” may mean information including a luminance         (luma) component block, a chrominance (chroma) component block         corresponding thereto, and syntax elements for respective blocks         so that the unit is designated to be distinguished from a block.     -   The size and shape of a unit may be variously implemented.         Further, a unit may have any of various sizes and shapes. In         particular, the shapes of the unit may include not only a         square, but also a geometric figure that can be represented in         two dimensions (2D), such as a rectangle, a trapezoid, a         triangle, and a pentagon.     -   Further, unit information may include one or more of the type of         a unit, the size of a unit, the depth of a unit, the order of         encoding of a unit and the order of decoding of a unit, etc. For         example, the type of a unit may indicate one of a CU, a PU, a         residual unit and a TU.     -   One unit may be partitioned into sub-units, each having a         smaller size than that of the relevant unit.     -   Depth: A depth may denote the degree to which the unit is         partitioned. Further, the unit depth may indicate the level at         which the corresponding unit is present when units are         represented in a tree structure.     -   Unit partition information may include a depth indicating the         depth of a unit. A depth may indicate the number of times the         unit is partitioned and/or the degree to which the unit is         partitioned.     -   In a tree structure, it may be considered that the depth of a         root node is the smallest, and the depth of a leaf node is the         largest.     -   A single unit may be hierarchically partitioned into multiple         sub-units while having depth information based on a tree         structure. In other words, the unit and sub-units, generated by         partitioning the unit, may correspond to a node and child nodes         of the node, respectively. Each of the partitioned sub-units may         have a unit depth. Since the depth indicates the number of times         the unit is partitioned and/or the degree to which the unit is         partitioned, the partition information of the sub-units may         include information about the sizes of the sub-units.     -   In a tree structure, the top node may correspond to the initial         node before partitioning. The top node may be referred to as a         “root node”. Further, the root node may have a minimum depth         value. Here, the top node may have a depth of level ‘0’.     -   A node having a depth of level ‘1’ may denote a unit generated         when the initial unit is partitioned once. A node having a depth         of level ‘2’ may denote a unit generated when the initial unit         is partitioned twice.     -   A leaf node having a depth of level ‘n’ may denote a unit         generated when the initial unit has been partitioned n times.     -   The leaf node may be a bottom node, which cannot be partitioned         any further. The depth of the leaf node may be the maximum         level. For example, a predefined value for the maximum level may         be 3.     -   A QT depth may denote a depth for a quad-partitioning. A BT         depth may denote a depth for a binary-partitioning. A TT depth         may denote a depth for a ternary-partitioning.

Sample: A sample may be a base unit constituting a block. A sample may be represented by values from 0 to 2^(Bd-)1 depending on the bit depth (Bd).

-   -   A sample may be a pixel or a pixel value.     -   Hereinafter, the terms “pixel” and “sample” may be used to have         the same meaning, and may be used interchangeably with each         other.

A Coding Tree Unit (CTU): A CTU may be composed of a single luma component (Y) coding tree block and two chroma component (Cb, Cr) coding tree blocks related to the luma component coding tree block. Further, a CTU may mean information including the above blocks and a syntax element for each of the blocks.

-   -   Each coding tree unit (CTU) may be partitioned using one or more         partitioning methods, such as a quad tree (QT), a binary tree         (BT), and a ternary tree (TT) so as to configure sub-units, such         as a coding unit, a prediction unit, and a transform unit.         Further, each coding tree unit may be partitioned using a         multitype tree (MTT) using one or more partitioning methods.     -   “CTU” may be used as a term designating a pixel block, which is         a processing unit in an image-decoding and encoding process, as         in the case of partitioning of an input image.

Coding Tree Block (CTB): “CTB” may be used as a term designating any one of a Y coding tree block, a Cb coding tree block, and a Cr coding tree block.

Neighbor block: A neighbor block (or neighboring block) may mean a block adjacent to a target block. A neighbor block may mean a reconstructed neighbor block.

Hereinafter, the terms “neighbor block” and “adjacent block” may be used to have the same meaning and may be used interchangeably with each other.

Spatial neighbor block; A spatial neighbor block may a block spatially adjacent to a target block. A neighbor block may include a spatial neighbor block.

-   -   The target block and the spatial neighbor block may be included         in a target picture.     -   The spatial neighbor block may mean a block, the boundary of         which is in contact with the target block, or a block located         within a predetermined distance from the target block.     -   The spatial neighbor block may mean a block adjacent to the         vertex of the target block. Here, the block adjacent to the         vertex of the target block may mean a block vertically adjacent         to a neighbor block which is horizontally adjacent to the target         block or a block horizontally adjacent to a neighbor block which         is vertically adjacent to the target block.

Temporal neighbor block: A temporal neighbor block may be a block temporally adjacent to a target block. A neighbor block may include a temporal neighbor block.

-   -   The temporal neighbor block may include a co-located block (col         block).     -   The col block may be a block in a previously reconstructed         co-located picture (col picture). The location of the col block         in the col-picture may correspond to the location of the target         block in a target picture. Alternatively, the location of the         col block in the col-picture may be equal to the location of the         target block in the target picture. The col picture may be a         picture included in a reference picture list.     -   The temporal neighbor block may be a block temporally adjacent         to a spatial neighbor block of a target block.

Prediction unit: A prediction unit may be a base unit for prediction, such as inter prediction, intra prediction, inter compensation, intra compensation, and motion compensation.

-   -   A single prediction unit may be divided into multiple partitions         having smaller sizes or sub-prediction units. The multiple         partitions may also be base units in the performance of         prediction or compensation. The partitions generated by dividing         the prediction unit may also be prediction units.

Prediction unit partition: A prediction unit partition may be the shape into which a prediction unit is divided.

Reconstructed neighboring unit: A reconstructed neighboring unit may be a unit which has already been decoded and reconstructed around a target unit.

-   -   A reconstructed neighboring unit may be a unit that is spatially         adjacent to the target unit or that is temporally adjacent to         the target unit.     -   A reconstructed spatially neighboring unit may be a unit which         is included in a target picture and which has already been         reconstructed through encoding and/or decoding.     -   A reconstructed temporally neighboring unit may be a unit which         is included in a reference image and which has already been         reconstructed through encoding and/or decoding. The location of         the reconstructed temporally neighboring unit in the reference         image may be identical to that of the target unit in the target         picture, or may correspond to the location of the target unit in         the target picture.

Parameter set: A parameter set may be header information in the structure of a bitstream. For example, a parameter set may include a video parameter set (VPS), a sequence parameter set (SPS), a picture parameter set (PPS), an adaptation parameter set (APS), etc.

Further, the parameter set may include slice header information and tile header information.

Rate-distortion optimization: An encoding apparatus may use rate-distortion optimization so as to provide high coding efficiency by utilizing combinations of the size of a coding unit (CU), a prediction mode, the size of a prediction unit (PU), motion information, and the size of a transform unit (TU).

-   -   A rate-distortion optimization scheme may calculate         rate-distortion costs of respective combinations so as to select         an optimal combination from among the combinations. The         rate-distortion costs may be calculated using the following         Equation 1. Generally, a combination enabling the         rate-distortion cost to be minimized may be selected as the         optimal combination in the rate-distortion optimization scheme.

D+λ*R  [Equation 1]

-   -   D may denote distortion. D may be the mean of squares of         differences (i.e. mean square error) between original transform         coefficients and reconstructed transform coefficients in a         transform unit.     -   R may denote the rate, which may denote a bit rate using         related-context information.     -   λ denotes a Lagrangian multiplier. R may include not only coding         parameter information, such as a prediction mode, motion         information, and a coded block flag, but also bits generated due         to the encoding of transform coefficients.     -   An encoding apparatus may perform procedures, such as inter         prediction and/or intra prediction, transform, quantization,         entropy encoding, inverse quantization (dequantization), and         inverse transform so as to calculate precise D and R. These         procedures may greatly increase the complexity of the encoding         apparatus.     -   Bitstream: A bitstream may denote a stream of bits including         encoded image information.     -   Parameter set: A parameter set may be header information in the         structure of a bitstream.     -   The parameter set may include at least one of a video parameter         set, a sequence parameter set, a picture parameter set, and an         adaptation parameter set. Further, the parameter set may include         information about a slice header and information about a tile         header.

Parsing: Parsing may be the decision on the value of a syntax element, made by performing entropy decoding on a bitstream. Alternatively, the term “parsing” may mean such entropy decoding itself.

Symbol: A symbol may be at least one of the syntax element, the coding parameter, and the transform coefficient of an encoding target unit and/or a decoding target unit. Further, a symbol may be the target of entropy encoding or the result of entropy decoding.

Reference picture: A reference picture may be an image referred to by a unit so as to perform inter prediction or motion compensation. Alternatively, a reference picture may be an image including a reference unit referred to by a target unit so as to perform inter prediction or motion compensation.

Hereinafter, the terms “reference picture” and “reference image” may be used to have the same meaning, and may be used interchangeably with each other.

Reference picture list: A reference picture list may be a list including one or more reference images used for inter prediction or motion compensation.

-   -   The types of a reference picture list may include List Combined         (LC), List 0 (L0), List 1 (L1), List 2 (L2), List 3 (L3), etc.     -   For inter prediction, one or more reference picture lists may be         used.

Inter-prediction indicator: An inter-prediction indicator may indicate the inter-prediction direction for a target unit. Inter prediction may be one of unidirectional prediction and bidirectional prediction. Alternatively, the inter-prediction indicator may denote the number of reference images used to generate a prediction unit of a target unit. Alternatively, the inter-prediction indicator may denote the number of prediction blocks used for inter prediction or motion compensation of a target unit.

Reference picture index: A reference picture index may be an index indicating a specific reference image in a reference picture list.

Motion vector (MV): A motion vector may be a 2D vector used for inter prediction or motion compensation. A motion vector may mean an offset between a target image and a reference image.

-   -   For example, a MV may be represented in a form such as (mv_(x),         mv_(y)). mv_(x) may indicate a horizontal component, and mv_(y)         may indicate a vertical component.     -   Search range: A search range may be a 2D area in which a search         for a MV is performed during inter prediction. For example, the         size of the search range may be M×N. M and N may be respective         positive integers.

Motion vector candidate: A motion vector candidate may be a block that is a prediction candidate or the motion vector of the block that is a prediction candidate when a motion vector is predicted.

-   -   A motion vector candidate may be included in a motion vector         candidate list.

Motion vector candidate list: A motion vector candidate list may be a list configured using one or more motion vector candidates.

Motion vector candidate index: A motion vector candidate index may be an indicator for indicating a motion vector candidate in the motion vector candidate list. Alternatively, a motion vector candidate index may be the index of a motion vector predictor.

Motion information: Motion information may be information including at least one of a reference picture list, a reference image, a motion vector candidate, a motion vector candidate index, a merge candidate, and a merge index, as well as a motion vector, a reference picture index, and an inter-prediction indicator.

Merge candidate list: A merge candidate list may be a list configured using merge candidates.

Merge candidate: A merge candidate may be a spatial merge candidate, a temporal merge candidate, a combined merge candidate, a combined bi-prediction merge candidate, a zero-merge candidate, etc. A merge candidate may include motion information such as prediction type information, a reference picture index for each list, and a motion vector.

Merge index: A merge index may be an indicator for indicating a merge candidate in a merge candidate list.

-   -   A merge index may indicate a reconstructed unit used to derive a         merge candidate between a reconstructed unit spatially adjacent         to a target unit and a reconstructed unit temporally adjacent to         the target unit.     -   A merge index may indicate at least one of pieces of motion         information of a merge candidate.

Transform unit: A transform unit may be the base unit of residual signal encoding and/or residual signal decoding, such as transform, inverse transform, quantization, dequantization, transform coefficient encoding, and transform coefficient decoding. A single transform unit may be partitioned into multiple transform units having smaller sizes.

Scaling: Scaling may denote a procedure for multiplying a factor by a transform coefficient level.

-   -   As a result of scaling of the transform coefficient level, a         transform coefficient may be generated. Scaling may also be         referred to as “dequantization”.

Quantization Parameter (QP): A quantization parameter may be a value used to generate a transform coefficient level for a transform coefficient in quantization. Alternatively, a quantization parameter may also be a value used to generate a transform coefficient by scaling the transform coefficient level in dequantization. Alternatively, a quantization parameter may be a value mapped to a quantization step size.

Delta quantization parameter: A delta quantization parameter is a difference value between a predicted quantization parameter and the quantization parameter of a target unit.

Scan: Scan may denote a method for aligning the order of coefficients in a unit, a block or a matrix. For example, a method for aligning a 2D array in the form of a one-dimensional (1D) array may be referred to as a “scan”. Alternatively, a method for aligning a 1D array in the form of a 2D array may also be referred to as a “scan” or an “inverse scan”.

Transform coefficient: A transform coefficient may be a coefficient value generated as an encoding apparatus performs a transform. Alternatively, the transform coefficient may be a coefficient value generated as a decoding apparatus performs at least one of entropy decoding and dequantization.

-   -   A quantized level or a quantized transform coefficient level         generated by applying quantization to a transform coefficient or         a residual signal may also be included in the meaning of the         term “transform coefficient”.

Quantized level: A quantized level may be a value generated as the encoding apparatus performs quantization on a transform coefficient or a residual signal. Alternatively, the quantized level may be a value that is the target of dequantization as the decoding apparatus performs dequantization.

-   -   A quantized transform coefficient level, which is the result of         transform and quantization, may also be included in the meaning         of a quantized level.

Non-zero transform coefficient: A non-zero transform coefficient may be a transform coefficient having a value other than 0 or a transform coefficient level having a value other than 0. Alternatively, a non-zero transform coefficient may be a transform coefficient, the magnitude of the value of which is not 0, or a transform coefficient level, the magnitude of the value of which is not 0.

Quantization matrix: A quantization matrix may be a matrix used in a quantization procedure or a dequantization procedure so as to improve the subjective image quality or objective image quality of an image. A quantization matrix may also be referred to as a “scaling list”.

Quantization matrix coefficient: A quantization matrix coefficient may be each element in a quantization matrix. A quantization matrix coefficient may also be referred to as a “matrix coefficient”.

Default matrix: A default matrix may be a quantization matrix predefined by the encoding apparatus and the decoding apparatus.

Non-default matrix: A non-default matrix may be a quantization matrix that is not predefined by the encoding apparatus and the decoding apparatus. The non-default matrix may be signaled by the encoding apparatus to the decoding apparatus.

Most Probable Mode (MPM): An MPM may denote an intra-prediction mode having a high probability of being used for intra prediction for a target block.

An encoding apparatus and a decoding apparatus may determine one or more MPMs based on coding parameters related to the target block and the attributes of entities related to the target block.

The encoding apparatus and the decoding apparatus may determine one or more MPMs based on the intra-prediction mode of a reference block. The reference block may include multiple reference blocks. The multiple reference blocks may include spatial neighbor blocks adjacent to the left of the target block and spatial neighbor blocks adjacent to the top of the target block. In other words, depending on which intra-prediction modes have been used for the reference blocks, one or more different MPMs may be determined.

The one or more MPMs may be determined in the same manner both in the encoding apparatus and in the decoding apparatus. That is, the encoding apparatus and the decoding apparatus may share the same MPM list including one or more MPMs.

MPM list: An MPM list may be a list including one or more MPMs. The number of the one or more MPMs in the MPM list may be defined in advance.

MPM indicator: An MPM indicator may indicate an MPM to be used for intra prediction for a target block among one or more MPMs in the MPM list. For example, the MPM indicator may be an index for the MPM list.

Since the MPM list is determined in the same manner both in the encoding apparatus and in the decoding apparatus, there may be no need to transmit the MPM list itself from the encoding apparatus to the decoding apparatus.

The MPM indicator may be signaled from the encoding apparatus to the decoding apparatus. As the MPM indicator is signaled, the decoding apparatus may determine the MPM to be used for intra prediction for the target block among the MPMs in the MPM list.

MPM use indicator: An MPM use indicator may indicate whether an MPM usage mode is to be used for prediction for a target block. The MPM usage mode may be a mode in which the MPM to be used for intra prediction for the target block is determined using the MPM list.

The MPM usage indicator may be signaled from the encoding apparatus to the decoding apparatus.

Signaling: “signaling” may denote that information is transferred from an encoding apparatus to a decoding apparatus. Alternatively, “signaling” may mean information is included in in a bitstream or a recoding medium. Information signaled by an encoding apparatus may be used by a decoding apparatus.

FIG. 1 is a block diagram illustrating the configuration of an embodiment of an encoding apparatus to which the present disclosure is applied.

An encoding apparatus 100 may be an encoder, a video encoding apparatus or an image encoding apparatus. A video may include one or more images (pictures). The encoding apparatus 100 may sequentially encode one or more images of the video.

Referring to FIG. 1, the encoding apparatus 100 includes an inter-prediction unit 110, an intra-prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, a dequantization (inverse quantization) unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190.

The encoding apparatus 100 may perform encoding on a target image using an intra mode and/or an inter mode.

Further, the encoding apparatus 100 may generate a bitstream, including information about encoding, via encoding on the target image, and may output the generated bitstream. The generated bitstream may be stored in a computer-readable storage medium and may be streamed through a wired/wireless transmission medium.

When the intra mode is used as a prediction mode, the switch 115 may switch to the intra mode. When the inter mode is used as a prediction mode, the switch 115 may switch to the inter mode.

The encoding apparatus 100 may generate a prediction block of a target block. Further, after the prediction block has been generated, the encoding apparatus 100 may encode a residual between the target block and the prediction block.

When the prediction mode is the intra mode, the intra-prediction unit 120 may use pixels of previously encoded/decoded neighboring blocks around the target block as reference samples. The intra-prediction unit 120 may perform spatial prediction on the target block using the reference samples, and may generate prediction samples for the target block via spatial prediction.

The inter-prediction unit 110 may include a motion prediction unit and a motion compensation unit.

When the prediction mode is an inter mode, the motion prediction unit may search a reference image for the area most closely matching the target block in a motion prediction procedure, and may derive a motion vector for the target block and the found area based on the found area.

The reference image may be stored in the reference picture buffer 190. More specifically, the reference image may be stored in the reference picture buffer 190 when the encoding and/or decoding of the reference image have been processed.

The motion compensation unit may generate a prediction block for the target block by performing motion compensation using a motion vector. Here, the motion vector may be a two-dimensional (2D) vector used for inter-prediction. Further, the motion vector may indicate an offset between the target image and the reference image.

The motion prediction unit and the motion compensation unit may generate a prediction block by applying an interpolation filter to a partial area of a reference image when the motion vector has a value other than an integer. In order to perform inter prediction or motion compensation, it may be determined which one of a skip mode, a merge mode, an advanced motion vector prediction (AMVP) mode, and a current picture reference mode corresponds to a method for predicting the motion of a PU included in a CU, based on the CU, and compensating for the motion, and inter prediction or motion compensation may be performed depending on the mode.

The subtractor 125 may generate a residual block, which is the differential between the target block and the prediction block. A residual block may also be referred to as a “residual signal”.

The residual signal may be the difference between an original signal and a prediction signal. Alternatively, the residual signal may be a signal generated by transforming or quantizing the difference between an original signal and a prediction signal or by transforming and quantizing the difference. A residual block may be a residual signal for a block unit.

The transform unit 130 may generate a transform coefficient by transforming the residual block, and may output the generated transform coefficient. Here, the transform coefficient may be a coefficient value generated by transforming the residual block.

The transform unit 130 may use one of multiple predefined transform methods when performing a transform.

The multiple predefined transform methods may include a Discrete Cosine Transform (DCT), a Discrete Sine Transform (DST), a Karhunen-Loeve Transform (KLT), etc.

The transform method used to transform a residual block may be determined depending on at least one of coding parameters for a target block and/or a neighboring block. For example, the transform method may be determined based on at least one of an inter-prediction mode for a PU, an intra-prediction mode for a PU, the size of a TU, and the shape of a TU. Alternatively, transformation information indicating the transform method may be signaled from the encoding apparatus 100 to the decoding apparatus 200.

When a transform skip mode is used, the transform unit 130 may omit transforming the residual block.

By applying quantization to the transform coefficient, a quantized transform coefficient level or a quantized level may be generated. Hereinafter, in the embodiments, each of the quantized transform coefficient level and the quantized level may also be referred to as a ‘transform coefficient’.

The quantization unit 140 may generate a quantized transform coefficient level (i.e., a quantized level or a quantized coefficient) by quantizing the transform coefficient depending on quantization parameters. The quantization unit 140 may output the quantized transform coefficient level that is generated. In this case, the quantization unit 140 may quantize the transform coefficient using a quantization matrix.

The entropy encoding unit 150 may generate a bitstream by performing probability distribution-based entropy encoding based on values, calculated by the quantization unit 140, and/or coding parameter values, calculated in the encoding procedure. The entropy encoding unit 150 may output the generated bitstream.

The entropy encoding unit 150 may perform entropy encoding on information about the pixels of the image and information required to decode the image. For example, the information required to decode the image may include syntax elements or the like.

When entropy encoding is applied, fewer bits may be assigned to more frequently occurring symbols, and more bits may be assigned to rarely occurring symbols. As symbols are represented by means of this assignment, the size of a bit string for target symbols to be encoded may be reduced. Therefore, the compression performance of video encoding may be improved through entropy encoding.

Further, for entropy encoding, the entropy encoding unit 150 may use a coding method such as exponential Golomb, Context-Adaptive Variable Length Coding (CAVLC), or Context-Adaptive Binary Arithmetic Coding (CABAC). For example, the entropy encoding unit 150 may perform entropy encoding using a Variable Length Coding/Code (VLC) table. For example, the entropy encoding unit 150 may derive a binarization method for a target symbol. Further, the entropy encoding unit 150 may derive a probability model for a target symbol/bin. The entropy encoding unit 150 may perform arithmetic coding using the derived binarization method, a probability model, and a context model.

The entropy encoding unit 150 may transform the coefficient of the form of a 2D block into the form of a 1D vector through a transform coefficient scanning method so as to encode a quantized transform coefficient level.

The coding parameters may be information required for encoding and/or decoding. The coding parameters may include information encoded by the encoding apparatus 100 and transferred from the encoding apparatus 100 to a decoding apparatus, and may also include information that may be derived in the encoding or decoding procedure. For example, information transferred to the decoding apparatus may include syntax elements.

The coding parameters may include not only information (or a flag or an index), such as a syntax element, which is encoded by the encoding apparatus and is signaled by the encoding apparatus to the decoding apparatus, but also information derived in an encoding or decoding process. Further, the coding parameters may include information required so as to encode or decode images. For example, the coding parameters may include at least one value, combinations or statistics of the size of a unit/block, the depth of a unit/block, partition information of a unit/block, the partition structure of a unit/block, information indicating whether a unit/block is partitioned in a quad-tree structure, information indicating whether a unit/block is partitioned in a binary tree structure, the partitioning direction of a binary tree structure (horizontal direction or vertical direction), the partitioning form of a binary tree structure (symmetrical partitioning or asymmetrical partitioning), information indicating whether a unit/block is partitioned in a ternary tree structure, the partitioning direction of a ternary tree structure (horizontal direction or vertical direction), the partitioning form of a ternary tree structure (symmetrical partitioning or asymmetrical partitioning, etc.), information indicating whether a unit/block is partitioned in a complex tree structure, a combination and a direction (horizontal direction or vertical direction, etc.) of a partitioning of the complex tree structure, a prediction scheme (intra prediction or inter prediction), an intra-prediction mode/direction, a reference sample filtering method, a prediction block filtering method, a prediction block boundary filtering method, a filter tap for filtering, a filter coefficient for filtering, an inter-prediction mode, motion information, a motion vector, a reference picture index, an inter-prediction direction, an inter-prediction indicator, a reference picture list, a reference image, a motion vector predictor, a motion vector prediction candidate, a motion vector candidate list, information indicating whether a merge mode is used, a merge candidate, a merge candidate list, information indicating whether a skip mode is used, the type of an interpolation filter, the tap of an interpolation filter, the filter coefficient of an interpolation filter, the magnitude of a motion vector, accuracy of motion vector representation, a transform type, a transform size, information indicating whether a first transform is used, information indicating whether an additional (secondary) transform is used, first transform selection information (or a first transform index), secondary transform selection information (or a secondary transform index), information indicating the presence or absence of a residual signal, a coded block pattern, a coded block flag, a quantization parameter, a quantization matrix, information about an intra-loop filter, information indicating whether an intra-loop filter is applied, the coefficient of an intra-loop filter, the tap of an intra-loop filter, the shape/form of an intra-loop filter, information indicating whether a deblocking filter is applied, the coefficient of a deblocking filter, the tap of a deblocking filter, deblocking filter strength, the shape/form of a deblocking filter, information indicating whether an adaptive sample offset is applied, the value of an adaptive sample offset, the category of an adaptive sample offset, the type of an adaptive sample offset, information indicating whether an adaptive in-loop filter is applied, the coefficient of an adaptive in-loop filter, the tap of an adaptive in-loop filter, the shape/form of an adaptive in-loop filter, a binarization/inverse binarization method, a context model, a context model decision method, a context model update method, information indicating whether a regular mode is performed, information whether a bypass mode is performed, a context bin, a bypass bin, a transform coefficient, a transform coefficient level, a transform coefficient level scanning method, an image display/output order, slice identification information, a slice type, slice partition information, tile identification information, a tile type, tile partition information, a picture type, bit depth, information about a luma signal, and information about a chroma signal. The prediction scheme may denote one prediction mode of an intra prediction mode and an inter prediction mode

The first transform selection information may indicate a first transform which is applied to a target block.

The second transform selection information may indicate a second transform which is applied to a target block.

The residual signal may denote the difference between the original signal and a prediction signal. Alternatively, the residual signal may be a signal generated by transforming the difference between the original signal and the prediction signal. Alternatively, the residual signal may be a signal generated by transforming and quantizing the difference between the original signal and the prediction signal. A residual block may be the residual signal for a block.

Here, signaling a flag or an index may mean that the encoding apparatus 100 includes an entropy-encoded flag or an entropy-encoded index, generated by performing entropy encoding on the flag or index, in a bitstream, and that the decoding apparatus 200 acquires a flag or an index by performing entropy decoding on the entropy-encoded flag or the entropy-encoded index, extracted from the bitstream.

Since the encoding apparatus 100 performs encoding via inter prediction, the encoded target image may be used as a reference image for additional image(s) to be subsequently processed. Therefore, the encoding apparatus 100 may reconstruct or decode the encoded target image and store the reconstructed or decoded image as a reference image in the reference picture buffer 190. For decoding, dequantization and inverse transform on the encoded target image may be processed.

The quantized level may be inversely quantized by the dequantization unit 160, and may be inversely transformed by the inverse transform unit 170. The dequantization unit 160 may generate an inversely quantized coefficient by performing inverse transform for the quantized level. The inverse transform unit 170 may generate a reconstructed residual block by performing inverse transform for the inversely quantized coefficient. In other words, the reconstructed residual block is a coefficient that has been inversely quantized and inversely transformed. The coefficient that has been inversely quantized and inversely transformed may be added to the prediction block by the adder 175. The inversely quantized and/or inversely transformed coefficient and the prediction block are added, and then a reconstructed block may be generated. Here, the inversely quantized and/or inversely transformed coefficient may denote a coefficient on which one or more of dequantization and inverse transform are performed, and may also denote a reconstructed residual block.

The reconstructed block may be subjected to filtering through the filter unit 180. The filter unit 180 may apply one or more of a deblocking filter, a Sample Adaptive Offset (SAO) filter, an Adaptive Loop Filter (ALF), and a Non Local Filter (NLF) to the reconstructed block or a reconstructed picture. The filter unit 180 may also be referred to as an “in-loop filter”.

The deblocking filter may eliminate block distortion occurring at the boundaries between blocks. In order to determine whether to apply the deblocking filter, the number of columns or rows which are included in a block and which include pixel(s) based on which it is determined whether to apply the deblocking filter to a target block may be decided on.

When the deblocking filter is applied to the target block, the applied filter may differ depending on the strength of the required deblocking filtering. In other words, among different filters, a filter decided on in consideration of the strength of deblocking filtering may be applied to the target block. When a deblocking filter is applied to a target block, a filter corresponding to any one of a strong filter and a weak filter may be applied to the target block depending on the strength of required deblocking filtering.

Also, when vertical filtering and horizontal filtering are performed on the target block, the horizontal filtering and the vertical filtering may be processed in parallel.

The SAO may add a suitable offset to the values of pixels to compensate for coding error. The SAO may perform, for the image to which deblocking is applied, correction that uses an offset in the difference between an original image and the image to which deblocking is applied, on a pixel basis. To perform an offset correction for an image, a method for dividing the pixels included in the image into a certain number of regions, determining a region to which an offset is to be applied, among the divided regions, and applying an offset to the determined region may be used, and a method for applying an offset in consideration of edge information of each pixel may also be used.

The ALF may perform filtering based on a value obtained by comparing a reconstructed image with an original image. After pixels included in an image have been divided into a predetermined number of groups, filters to be applied to each group may be determined, and filtering may be differentially performed for respective groups. For a luma signal, information related to whether to apply an adaptive loop filter may be signaled for each CU. The shapes and filter coefficients of ALFs to be applied to respective blocks may differ for respective blocks. Alternatively, regardless of the features of a block, an ALF having a fixed form may be applied to the block.

A non-local filter may perform filtering based on reconstructed blocks, similar to a target block. A region similar to the target block may be selected from a reconstructed picture, and filtering of the target block may be performed using the statistical properties of the selected similar region. Information about whether to apply a non-local filter may be signaled for a Coding Unit (CU). Also, the shapes and filter coefficients of the non-local filter to be applied to blocks may differ depending on the blocks.

The reconstructed block or the reconstructed image subjected to filtering through the filter unit 180 may be stored in the reference picture buffer 190. The reconstructed block subjected to filtering through the filter unit 180 may be a part of a reference picture. In other words, the reference picture may be a reconstructed picture composed of reconstructed blocks subjected to filtering through the filter unit 180. The stored reference picture may be subsequently used for inter prediction.

FIG. 2 is a block diagram illustrating the configuration of an embodiment of a decoding apparatus to which the present disclosure is applied.

A decoding apparatus 200 may be a decoder, a video decoding apparatus or an image decoding apparatus.

Referring to FIG. 2, the decoding apparatus 200 may include an entropy decoding unit 210, a dequantization (inverse quantization) unit 220, an inverse transform unit 230, an intra-prediction unit 240, an inter-prediction unit 250, a switch 245 an adder 255, a filter unit 260, and a reference picture buffer 270.

The decoding apparatus 200 may receive a bitstream output from the encoding apparatus 100. The decoding apparatus 200 may receive a bitstream stored in a computer-readable storage medium, and may receive a bitstream that is streamed through a wired/wireless transmission medium.

The decoding apparatus 200 may perform decoding on the bitstream in an intra mode and/or an inter mode. Further, the decoding apparatus 200 may generate a reconstructed image or a decoded image via decoding, and may output the reconstructed image or decoded image.

For example, switching to an intra mode or an inter mode based on the prediction mode used for decoding may be performed by the switch 245. When the prediction mode used for decoding is an intra mode, the switch 245 may be operated to switch to the intra mode. When the prediction mode used for decoding is an inter mode, the switch 245 may be operated to switch to the inter mode.

The decoding apparatus 200 may acquire a reconstructed residual block by decoding the input bitstream, and may generate a prediction block. When the reconstructed residual block and the prediction block are acquired, the decoding apparatus 200 may generate a reconstructed block, which is the target to be decoded, by adding the reconstructed residual block to the prediction block.

The entropy decoding unit 210 may generate symbols by performing entropy decoding on the bitstream based on the probability distribution of a bitstream. The generated symbols may include symbols in a form of a quantized transform coefficient level (i.e., a quantized level or a quantized coefficient). Here, the entropy decoding method may be similar to the above-described entropy encoding method. That is, the entropy decoding method may be the reverse procedure of the above-described entropy encoding method.

The entropy decoding unit 210 may change a coefficient having a one-dimensional (1D) vector form to a 2D block shape through a transform coefficient scanning method in order to decode a quantized transform coefficient level.

For example, the coefficients of the block may be changed to 2D block shapes by scanning the block coefficients using up-right diagonal scanning. Alternatively, which one of up-right diagonal scanning, vertical scanning, and horizontal scanning is to be used may be determined depending on the size and/or the intra-prediction mode of the corresponding block.

The quantized coefficient may be inversely quantized by the dequantization unit 220. The dequantization unit 220 may generate an inversely quantized coefficient by performing dequantization on the quantized coefficient. Further, the inversely quantized coefficient may be inversely transformed by the inverse transform unit 230. The inverse transform unit 230 may generate a reconstructed residual block by performing an inverse transform on the inversely quantized coefficient. As a result of performing dequantization and the inverse transform on the quantized coefficient, the reconstructed residual block may be generated. Here, the dequantization unit 220 may apply a quantization matrix to the quantized coefficient when generating the reconstructed residual block.

When the intra mode is used, the intra-prediction unit 240 may generate a prediction block by performing spatial prediction that uses the pixel values of previously decoded neighboring blocks around a target block.

The inter-prediction unit 250 may include a motion compensation unit. Alternatively, the inter-prediction unit 250 may be designated as a “motion compensation unit”.

When the inter mode is used, the motion compensation unit may generate a prediction block by performing motion compensation that uses a motion vector and a reference image stored in the reference picture buffer 270.

The motion compensation unit may apply an interpolation filter to a partial area of the reference image when the motion vector has a value other than an integer, and may generate a prediction block using the reference image to which the interpolation filter is applied. In order to perform motion compensation, the motion compensation unit may determine which one of a skip mode, a merge mode, an Advanced Motion Vector Prediction (AMVP) mode, and a current picture reference mode corresponds to the motion compensation method used for a PU included in a CU, based on the CU, and may perform motion compensation depending on the determined mode.

The reconstructed residual block and the prediction block may be added to each other by the adder 255. The adder 255 may generate a reconstructed block by adding the reconstructed residual block to the prediction block.

The reconstructed block may be subjected to filtering through the filter unit 260. The filter unit 260 may apply at least one of a deblocking filter, an SAO filter, an ALF, and a NLF to the reconstructed block or the reconstructed image. The reconstructed image may be a picture including the reconstructed block.

The reconstructed image subjected to filtering may be outputted by the encoding apparatus 100, and may be used by the encoding apparatus.

The reconstructed image subjected to filtering through the filter unit 260 may be stored as a reference picture in the reference picture buffer 270. The reconstructed block subjected to filtering through the filter unit 260 may be a part of the reference picture. In other words, the reference picture may be an image composed of reconstructed blocks subjected to filtering through the filter unit 260. The stored reference picture may be subsequently used for inter prediction.

FIG. 3 is a diagram schematically illustrating the partition structure of an image when the image is encoded and decoded.

FIG. 3 may schematically illustrate an example in which a single unit is partitioned into multiple sub-units.

In order to efficiently partition the image, a Coding Unit (CU) may be used in encoding and decoding. The term “unit” may be used to collectively designate 1) a block including image samples and 2) a syntax element. For example, the “partitioning of a unit” may mean the “partitioning of a block corresponding to a unit”.

A CU may be used as a base unit for image encoding/decoding. A CU may be used as a unit to which one mode selected from an intra mode and an inter mode in image encoding/decoding is applied. In other words, in image encoding/decoding, which one of an intra mode and an inter mode is to be applied to each CU may be determined.

Further, a CU may be a base unit in prediction, transform, quantization, inverse transform, dequantization, and encoding/decoding of transform coefficients.

Referring to FIG. 3, an image 200 may be sequentially partitioned into units corresponding to a Largest Coding Unit (LCU), and a partition structure may be determined for each LCU. Here, the LCU may be used to have the same meaning as a Coding Tree Unit (CTU).

The partitioning of a unit may mean the partitioning of a block corresponding to the unit. Block partition information may include depth information about the depth of a unit. The depth information may indicate the number of times the unit is partitioned and/or the degree to which the unit is partitioned. A single unit may be hierarchically partitioned into sub-units while having depth information based on a tree structure. Each of partitioned sub-units may have depth information. The depth information may be information indicating the size of a CU. The depth information may be stored for each CU.

Each CU may have depth information. When the CU is partitioned, CUs resulting from partitioning may have a depth increased from the depth of the partitioned CU by 1.

The partition structure may mean the distribution of Coding Units (CUs) to efficiently encode the image in an LCU 310. Such a distribution may be determined depending on whether a single CU is to be partitioned into multiple CUs. The number of CUs generated by partitioning may be a positive integer of 2 or more, including 2, 3, 4, 8, 16, etc. The horizontal size and the vertical size of each of CUs generated by the partitioning may be less than the horizontal size and the vertical size of a CU before being partitioned, depending on the number of CUs generated by partitioning.

Each partitioned CU may be recursively partitioned into four CUs in the same way. Via the recursive partitioning, at least one of the horizontal size and the vertical size of each partitioned CU may be reduced compared to at least one of the horizontal size and the vertical size of the CU before being partitioned.

The partitioning of a CU may be recursively performed up to a predefined depth or a predefined size. For example, the depth of a CU may have a value ranging from 0 to 3. The size of the CU may range from a size of 64×64 to a size of 8×8 depending on the depth of the CU.

For example, the depth of an LCU may be 0, and the depth of a Smallest Coding Unit (SCU) may be a predefined maximum depth. Here, as described above, the LCU may be the CU having the maximum coding unit size, and the SCU may be the CU having the minimum coding unit size.

Partitioning may start at the LCU 310, and the depth of a CU may be increased by 1 whenever the horizontal and/or vertical sizes of the CU are reduced by partitioning.

For example, for respective depths, a CU that is not partitioned may have a size of 2N×2N. Further, in the case of a CU that is partitioned, a CU having a size of 2N×2N may be partitioned into four CUs, each having a size of N×N. The value of N may be halved whenever the depth is increased by 1.

Referring to FIG. 3, an LCU having a depth of 0 may have 64×64 pixels or 64×64 blocks. 0 may be a minimum depth. An SCU having a depth of 3 may have 8×8 pixels or 8×8 blocks. 3 may be a maximum depth. Here, a CU having 64×64 blocks, which is the LCU, may be represented by a depth of 0. A CU having 32×32 blocks may be represented by a depth of 1. A CU having 16×16 blocks may be represented by a depth of 2. A CU having 8×8 blocks, which is the SCU, may be represented by a depth of 3.

Information about whether the corresponding CU is partitioned may be represented by the partition information of the CU. The partition information may be 1-bit information. All CUs except the SCU may include partition information. For example, the value of the partition information of a CU that is not partitioned may be 0. The value of the partition information of a CU that is partitioned may be 1.

For example, when a single CU is partitioned into four CUs, the horizontal size and vertical size of each of four CUs generated by partitioning may be half the horizontal size and the vertical size of the CU before being partitioned. When a CU having a 32×32 size is partitioned into four CUs, the size of each of four partitioned CUs may be 16×16. When a single CU is partitioned into four CUs, it may be considered that the CU has been partitioned in a quad-tree structure.

For example, when a single CU is partitioned into two CUs, the horizontal size or the vertical size of each of two CUs generated by partitioning may be half the horizontal size or the vertical size of the CU before being partitioned. When a CU having a 32×32 size is vertically partitioned into two CUs, the size of each of two partitioned CUs may be 16×32. When a CU having a 32×32 size is horizontally partitioned into two CUs, the size of each of two partitioned CUs may be 32×16. When a single CU is partitioned into two CUs, it may be considered that the CU has been partitioned in a binary-tree structure.

Both of quad-tree partitioning and binary-tree partitioning are applied to the LCU 310 of FIG. 3.

In the encoding apparatus 100, a Coding Tree Unit (CTU) having a size of 64×64 may be partitioned into multiple smaller CUs by a recursive quad-tree structure. A single CU may be partitioned into four CUs having the same size. Each CU may be recursively partitioned, and may have a quad-tree structure.

By the recursive partitioning of a CU, an optimal partitioning method that incurs a minimum rate-distortion cost may be selected.

FIG. 4 is a diagram illustrating the form of a Prediction Unit (PU) that a Coding Unit (CU) can include.

When, among CUs partitioned from an LCU, a CU, which is not partitioned any further, may be divided into one or more Prediction Units (PUs). Such division is also referred to as “partitioning”.

A PU may be a base unit for prediction. A PU may be encoded and decoded in any one of a skip mode, an inter mode, and an intra mode. A PU may be partitioned into various shapes depending on respective modes. For example, the target block, described above with reference to FIG. 1, and the target block, described above with reference to FIG. 2, may each be a PU.

A CU may not be split into PUs. When the CU is not split into PUs, the size of the CU and the size of a PU may be equal to each other.

In a skip mode, partitioning may not be present in a CU. In the skip mode, a 2N×2N mode 410, in which the sizes of a PU and a CU are identical to each other, may be supported without partitioning.

In an inter mode, 8 types of partition shapes may be present in a CU. For example, in the inter mode, the 2N×2N mode 410, a 2N×N mode 415, an N×2N mode 420, an N×N mode 425, a 2N×nU mode 430, a 2N×nD mode 435, an nL×2N mode 440, and an nR×2N mode 445 may be supported.

In an intra mode, the 2N×2N mode 410 and the N×N mode 425 may be supported.

In the 2N×2N mode 410, a PU having a size of 2N×2N may be encoded. The PU having a size of 2N×2N may mean a PU having a size identical to that of the CU. For example, the PU having a size of 2N×2N may have a size of 64×64, 32×32, 16×16 or 8×8.

In the N×N mode 425, a PU having a size of N×N may be encoded.

For example, in intra prediction, when the size of a PU is 8×8, four partitioned PUs may be encoded. The size of each partitioned PU may be 4×4.

When a PU is encoded in an intra mode, the PU may be encoded using any one of multiple intra-prediction modes. For example, HEVC technology may provide 35 intra-prediction modes, and the PU may be encoded in any one of the 35 intra-prediction modes.

Which one of the 2N×2N mode 410 and the N×N mode 425 is to be used to encode the PU may be determined based on rate-distortion cost.

The encoding apparatus 100 may perform an encoding operation on a PU having a size of 2N×2N. Here, the encoding operation may be the operation of encoding the PU in each of multiple intra-prediction modes that can be used by the encoding apparatus 100. Through the encoding operation, the optimal intra-prediction mode for a PU having a size of 2N×2N may be derived. The optimal intra-prediction mode may be an intra-prediction mode in which a minimum rate-distortion cost occurs upon encoding the PU having a size of 2N×2N, among multiple intra-prediction modes that can be used by the encoding apparatus 100.

Further, the encoding apparatus 100 may sequentially perform an encoding operation on respective PUs obtained from N×N partitioning. Here, the encoding operation may be the operation of encoding a PU in each of multiple intra-prediction modes that can be used by the encoding apparatus 100. By means of the encoding operation, the optimal intra-prediction mode for the PU having a size of N×N may be derived. The optimal intra-prediction mode may be an intra-prediction mode in which a minimum rate-distortion cost occurs upon encoding the PU having a size of N×N, among multiple intra-prediction modes that can be used by the encoding apparatus 100.

The encoding apparatus 100 may determine which of a PU having a size of 2N×2N and PUs having sizes of N×N to be encoded based on a comparison of a rate-distortion cost of the PU having a size of 2N×2N and a rate-distortion costs of the PUs having sizes of N×N.

A single CU may be partitioned into one or more PUs, and a PU may be partitioned into multiple PUs.

For example, when a single PU is partitioned into four PUs, the horizontal size and vertical size of each of four PUs generated by partitioning may be half the horizontal size and the vertical size of the PU before being partitioned. When a PU having a 32×32 size is partitioned into four PUs, the size of each of four partitioned PUs may be 16×16. When a single PU is partitioned into four PUs, it may be considered that the PU has been partitioned in a quad-tree structure.

For example, when a single PU is partitioned into two PUs, the horizontal size or the vertical size of each of two PUs generated by partitioning may be half the horizontal size or the vertical size of the PU before being partitioned. When a PU having a 32×32 size is vertically partitioned into two PUs, the size of each of two partitioned PUs may be 16×32. When a PU having a 32×32 size is horizontally partitioned into two PUs, the size of each of two partitioned PUs may be 32×16. When a single PU is partitioned into two PUs, it may be considered that the PU has been partitioned in a binary-tree structure.

FIG. 5 is a diagram illustrating the form of a Transform Unit (TU) that can be included in a CU.

A Transform Unit (TU) may have a base unit that is used for a procedure, such as transform, quantization, inverse transform, dequantization, entropy encoding, and entropy decoding, in a CU.

A TU may have a square shape or a rectangular shape. A shape of a TU may be determined based on a size and/or a shape of a CU.

Among CUs partitioned from the LCU, a CU which is not partitioned into CUs any further may be partitioned into one or more TUs. Here, the partition structure of a TU may be a quad-tree structure. For example, as shown in FIG. 5, a single CU 510 may be partitioned one or more times depending on the quad-tree structure. By means of this partitioning, the single CU 510 may be composed of TUs having various sizes.

It can be considered that when a single CU is split two or more times, the CU is recursively split. Through splitting, a single CU may be composed of Transform Units (TUs) having various sizes.

Alternatively, a single CU may be split into one or more TUs based on the number of vertical lines and/or horizontal lines that split the CU.

A CU may be split into symmetric TUs or asymmetric TUs. For splitting into asymmetric TUs, information about the size and/or shape of each TU may be signaled from the encoding apparatus 100 to the decoding apparatus 200. Alternatively, the size and/or shape of each TU may be derived from information about the size and/or shape of the CU.

A CU may not be split into TUs. When the CU is not split into TUs, the size of the CU and the size of a TU may be equal to each other.

A single CU may be partitioned into one or more TUs, and a TU may be partitioned into multiple TUs.

For example, when a single TU is partitioned into four TUs, the horizontal size and vertical size of each of four TUs generated by partitioning may be half the horizontal size and the vertical size of the TU before being partitioned. When a TU having a 32×32 size is partitioned into four TUs, the size of each of four partitioned TUs may be 16×16. When a single TU is partitioned into four TUs, it may be considered that the TU has been partitioned in a quad-tree structure.

For example, when a single TU is partitioned into two TUs, the horizontal size or the vertical size of each of two TUs generated by partitioning may be half the horizontal size or the vertical size of the TU before being partitioned. When a TU having a 32×32 size is vertically partitioned into two TUs, the size of each of two partitioned TUs may be 16×32. When a TU having a 32×32 size is horizontally partitioned into two TUs, the size of each of two partitioned TUs may be 32×16. When a single TU is partitioned into two TUs, it may be considered that the TU has been partitioned in a binary-tree structure.

In a way differing from that illustrated in FIG. 5, a CU may be split.

For example, a single CU may be split into three CUs. The horizontal sizes or vertical sizes of the three CUs generated from splitting may be ¼, ½, and ¼, respectively, of the horizontal size or vertical size of the original CU before being split.

For example, when a CU having a 32×32 size is vertically split into three CUs, the sizes of the three CUs generated from the splitting may be 8×32, 16×32, and 8×32, respectively. In this way, when a single CU is split into three CUs, it may be considered that the CU is split in the form of a ternary tree.

One of exemplary splitting forms, that is, quad-tree splitting, binary tree splitting, and ternary tree splitting, may be applied to the splitting of a CU, and multiple splitting schemes may be combined and used together for splitting of a CU. Here, the case where multiple splitting schemes are combined and used together may be referred to as “complex tree-format splitting”.

FIG. 6 illustrates the splitting of a block according to an example.

In a video encoding and/or decoding process, a target block may be split, as illustrated in FIG. 6.

For splitting of the target block, an indicator indicating split information may be signaled from the encoding apparatus 100 to the decoding apparatus 200. The split information may be information indicating how the target block is split.

The split information may be one or more of a split flag (hereinafter referred to as “split_flag”), a quad-binary flag (hereinafter referred to as “QB_flag”), a quad-tree flag (hereinafter referred to as “quadtree_flag”), a binary tree flag (hereinafter referred to as “binarytree_flag”), and a binary type flag (hereinafter referred to as “Btype_flag”).

“split_flag” may be a flag indicating whether a block is split. For example, a split_flag value of 1 may indicate that the corresponding block is split. A split_flag value of 0 may indicate that the corresponding block is not split.

“QB_flag” may be a flag indicating which one of a quad-tree form and a binary tree form corresponds to the shape in which the block is split. For example, a QB_flag value of 0 may indicate that the block is split in a quad-tree form. A QB_flag value of 1 may indicate that the block is split in a binary tree form. Alternatively, a QB_flag value of 0 may indicate that the block is split in a binary tree form. A QB_flag value of 1 may indicate that the block is split in a quad-tree form.

“quadtree_flag” may be a flag indicating whether a block is split in a quad-tree form. For example, a quadtree_flag value of 1 may indicate that the block is split in a quad-tree form. A quadtree_flag value of 0 may indicate that the block is not split in a quad-tree form.

“binarytree_flag” may be a flag indicating whether a block is split in a binary tree form. For example, a binarytree_flag value of 1 may indicate that the block is split in a binary tree form. A binarytree_flag value of 0 may indicate that the block is not split in a binary tree form.

“Btype_flag” may be a flag indicating which one of a vertical split and a horizontal split corresponds to a split direction when a block is split in a binary tree form. For example, a Btype_flag value of 0 may indicate that the block is split in a horizontal direction. A Btype_flag value of 1 may indicate that a block is split in a vertical direction. Alternatively, a Btype_flag value of 0 may indicate that the block is split in a vertical direction. A Btype_flag value of 1 may indicate that a block is split in a horizontal direction.

For example, the split information of the block in FIG. 6 may be derived by signaling at least one of quadtree_flag, binarytree_flag, and Btype_flag, as shown in the following Table 1.

TABLE 1 quadtree_flag binarytree_flag Btype_flag 1 0 1 1 0 0 1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1 1 0 0 0 0 0

For example, the split information of the block in FIG. 6 may be derived by signaling at least one of split_flag, QB_flag and Btype_flag, as shown in the following Table 2.

TABLE 2 split_flag QB_flag Btype_flag 1 0 1 1 1 0 0 1 0 1 1 0 0 0 0 0 0 1 1 0 1 1 0 0 0 0

The splitting method may be limited only to a quad-tree or to a binary tree depending on the size and/or shape of the block. When this limitation is applied, split_flag may be a flag indicating whether a block is split in a quad-tree form or a flag indicating whether a block is split in a binary tree form. The size and shape of a block may be derived depending on the depth information of the block, and the depth information may be signaled from the encoding apparatus 100 to the decoding apparatus 200.

When the size of a block falls within a specific range, only splitting in a quad-tree form may be possible. For example, the specific range may be defined by at least one of a maximum block size and a minimum block size at which only splitting in a quad-tree form is possible.

Information indicating the maximum block size and the minimum block size at which only splitting in a quad-tree form is possible may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. Further, this information may be signaled for at least one of units such as a video, a sequence, a picture, and a slice (or a segment).

Alternatively, the maximum block size and/or the minimum block size may be fixed sizes predefined by the encoding apparatus 100 and the decoding apparatus 200. For example, when the size of a block is above 64×64 and below 256×256, only splitting in a quad-tree form may be possible. In this case, split_flag may be a flag indicating whether splitting in a quad-tree form is performed.

When the size of a block falls within the specific range, only splitting in a binary tree form may be possible. For example, the specific range may be defined by at least one of a maximum block size and a minimum block size at which only splitting in a binary tree form is possible.

Information indicating the maximum block size and/or the minimum block size at which only splitting in a binary tree form is possible may be signaled from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. Further, this information may be signaled for at least one of units such as a sequence, a picture, and a slice (or a segment).

Alternatively, the maximum block size and/or the minimum block size may be fixed sizes predefined by the encoding apparatus 100 and the decoding apparatus 200. For example, when the size of a block is above 8×8 and below 16×16, only splitting in a binary tree form may be possible. In this case, split_flag may be a flag indicating whether splitting in a binary tree form is performed.

The splitting of a block may be limited by previous splitting. For example, when a block is split in a binary tree form and multiple partition blocks are generated, each partition block may be additionally split only in a binary tree form.

When the horizontal size or vertical size of a partition block is a size that cannot be split further, the above-described indicator may not be signaled.

FIG. 7 is a diagram for explaining an embodiment of an intra-prediction process.

Arrows radially extending from the center of the graph in FIG. 7 indicate the prediction directions of intra-prediction modes. Further, numbers appearing near the arrows indicate examples of mode values assigned to intra-prediction modes or to the prediction directions of the intra-prediction modes.

Intra encoding and/or decoding may be performed using reference samples of blocks neighboring a target block. The neighboring blocks may be neighboring reconstructed blocks. For example, intra encoding and/or decoding may be performed using the values of reference samples which are included in each neighboring reconstructed block or the coding parameters of the neighboring reconstructed block.

The encoding apparatus 100 and/or the decoding apparatus 200 may generate a prediction block by performing intra prediction on a target block based on information about samples in a target image. When intra prediction is performed, the encoding apparatus 100 and/or the decoding apparatus 200 may generate a prediction block for the target block by performing intra prediction based on information about samples in the target image. When intra prediction is performed, the encoding apparatus 100 and/or the decoding apparatus 200 may perform directional prediction and/or non-directional prediction based on at least one reconstructed reference sample.

A prediction block may be a block generated as a result of performing intra prediction. A prediction block may correspond to at least one of a CU, a PU, and a TU.

The unit of a prediction block may have a size corresponding to at least one of a CU, a PU, and a TU. The prediction block may have a square shape having a size of 2N×2N or N×N. The size of N×N may include sizes of 4×4, 8×8, 16×16, 32×32, 64×64, or the like.

Alternatively, a prediction block may a square block having a size of 2×2, 4×4, 8×8, 16×16, 32×32, 64×64 or the like or a rectangular block having a size of 2×8, 4×8, 2×16, 4×16, 8×16, or the like.

Intra prediction may be performed in consideration of the intra-prediction mode for the target block. The number of intra-prediction modes that the target block can have may be a predefined fixed value, and may be a value determined differently depending on the attributes of a prediction block. For example, the attributes of the prediction block may include the size of the prediction block, the type of prediction block, etc.

For example, the number of intra-prediction modes may be fixed at 35 regardless of the size of a prediction block. Alternatively, the number of intra-prediction modes may be, for example, 3, 5, 9, 17, 34, 35, or 36.

The intra-prediction modes may be non-directional modes or directional modes. For example, the intra-prediction modes may include two non-directional modes and 33 directional modes, as shown in FIG. 7.

The two non-directional modes may include a DC mode and a planar mode.

The directional modes may be prediction modes having a specific direction or a specific angle.

The intra-prediction modes may each be represented by at least one of a mode number, a mode value, and a mode angle. The number of intra-prediction modes may be M. The value of M may be 1 or more. In other words, the number of intra-prediction modes may be M, which includes the number of non-directional modes and the number of directional modes.

The number of intra-prediction modes may be fixed to M regardless of the size and/or the color component of a block. For example, the number of intra-prediction modes may be fixed at any one of 35 and 67 regardless of the size of a block.

Alternatively, the number of intra-prediction modes may differ depending on the size and/or the type of the color component of a block.

For example, the larger the size of the block, the greater the number of intra-prediction modes. Alternatively, the larger the size of the block, the smaller the number of intra-prediction modes. When the size of the block is 4×4 or 8×8, the number of intra-prediction modes may be 67. When the size of the block is 16×16, the number of intra-prediction modes may be 35. When the size of the block is 32×32, the number of intra-prediction modes may be 19. When the size of a block is 64×64, the number of intra-prediction modes may be 7.

For example, the number of intra prediction modes may differ depending on whether a color component is a luma signal or a chroma signal. Alternatively, the number of intra-prediction modes corresponding to a luma component block may be greater than the number of intra-prediction modes corresponding to a chroma component block.

For example, in a vertical mode having a mode value of 26, prediction may be performed in a vertical direction based on the pixel value of a reference sample. For example, in a horizontal mode having a mode value of 10, prediction may be performed in a horizontal direction based on the pixel value of a reference sample.

Even in directional modes other than the above-described mode, the encoding apparatus 100 and the decoding apparatus 200 may perform intra prediction on a target unit using reference samples depending on angles corresponding to the directional modes.

Intra-prediction modes located on a right side with respect to the vertical mode may be referred to as ‘vertical-right modes’. Intra-prediction modes located below the horizontal mode may be referred to as ‘horizontal-below modes’. For example, in FIG. 7, the intra-prediction modes in which a mode value is one of 27, 28, 29, 30, 31, 32, 33, and 34 may be vertical-right modes 613. Intra-prediction modes in which a mode value is one of 2, 3, 4, 5, 6, 7, 8, and 9 may be horizontal-below modes 616.

The non-directional mode may include a DC mode and a planar mode.

For example, a value of the DC mode may be 1. A value of the planar mode may be 0.

The directional mode may include an angular mode. Among the plurality of the intra prediction modes, remaining modes except for the DC mode and the planar mode may be directional modes.

When the intra-prediction mode is a DC mode, a prediction block may be generated based on the average of pixel values of a plurality of reference pixels. For example, a value of a pixel of a prediction block may be determined based on the average of pixel values of a plurality of reference pixels.

The number of above-described intra-prediction modes and the mode values of respective intra-prediction modes are merely exemplary. The number of above-described intra-prediction modes and the mode values of respective intra-prediction modes may be defined differently depending on the embodiments, implementation and/or requirements.

In order to perform intra prediction on a target block, the step of checking whether samples included in a reconstructed neighboring block can be used as reference samples of a target block may be performed. When a sample that cannot be used as a reference sample of the target block is present among samples in the neighboring block, a value generated via copying and/or interpolation that uses at least one sample value, among the samples included in the reconstructed neighboring block, may replace the sample value of the sample that cannot be used as the reference sample. When the value generated via copying and/or interpolation replaces the sample value of the existing sample, the sample may be used as the reference sample of the target block.

In intra prediction, a filter may be applied to at least one of a reference sample and a prediction sample based on at least one of the intra-prediction mode and the size of the target block.

The type of filter to be applied to at least one of a reference sample and a prediction sample may differ depending on at least one of the intra-prediction mode of a target block, the size of the target block, and the shape of the target block. The types of filters may be classified depending on one or more of the number of filter taps, the value of a filter coefficient, and filter strength.

When the intra-prediction mode is a planar mode, a sample value of a prediction target block may be generated using a weighted sum of an above reference sample of the target block, a left reference sample of the target block, an above-right reference sample of the target block, and a below-left reference sample of the target block depending on the location of the prediction target sample in the prediction block when the prediction block of the target block is generated.

When the intra-prediction mode is a DC mode, the average of reference samples above the target block and the reference samples to the left of the target block may be used when the prediction block of the target block is generated. Also, filtering using the values of reference samples may be performed on specific rows or specific columns in the target block. The specific rows may be one or more upper rows adjacent to the reference sample. The specific columns may be one or more left columns adjacent to the reference sample.

When the intra-prediction mode is a directional mode, a prediction block may be generated using the above reference samples, left reference samples, above-right reference sample and/or below-left reference sample of the target block.

In order to generate the above-described prediction sample, real-number-based interpolation may be performed.

The intra-prediction mode of the target block may be predicted from intra prediction mode of a neighboring block adjacent to the target block, and the information used for prediction may be entropy-encoded/decoded.

For example, when the intra-prediction modes of the target block and the neighboring block are identical to each other, it may be signaled, using a predefined flag, that the intra-prediction modes of the target block and the neighboring block are identical.

For example, an indicator for indicating an intra-prediction mode identical to that of the target block, among intra-prediction modes of multiple neighboring blocks, may be signaled.

When the intra-prediction modes of the target block and a neighboring block are different from each other, information about the intra-prediction mode of the target block may be encoded and/or decoded using entropy encoding and/or decoding.

FIG. 8 is a diagram for explaining the locations of reference samples used in an intra-prediction procedure.

FIG. 8 illustrates the locations of reference samples used for intra prediction of a target block. Referring to FIG. 8, reconstructed reference samples used for intra prediction of the target block may include below-left reference samples 831, left reference samples 833, an above-left corner reference sample 835, above reference samples 837, and above-right reference samples 839.

For example, the left reference samples 833 may mean reconstructed reference pixels adjacent to the left side of the target block. The above reference samples 837 may mean reconstructed reference pixels adjacent to the top of the target block. The above-left corner reference sample 835 may mean a reconstructed reference pixel located at the above-left corner of the target block. The below-left reference samples 831 may mean reference samples located below a left sample line composed of the left reference samples 833, among samples located on the same line as the left sample line. The above-right reference samples 839 may mean reference samples located to the right of an above sample line composed of the above reference samples 837, among samples located on the same line as the above sample line.

When the size of a target block is N×N, the numbers of the below-left reference samples 831, the left reference samples 833, the above reference samples 837, and the above-right reference samples 839 may each be N.

By performing intra prediction on the target block, a prediction block may be generated. The generation of the prediction block may include the determination of the values of pixels in the prediction block. The sizes of the target block and the prediction block may be equal.

The reference samples used for intra prediction of the target block may vary depending on the intra-prediction mode of the target block. The direction of the intra-prediction mode may represent a dependence relationship between the reference samples and the pixels of the prediction block. For example, the value of a specified reference sample may be used as the values of one or more specified pixels in the prediction block. In this case, the specified reference sample and the one or more specified pixels in the prediction block may be the sample and pixels which are positioned in a straight line in the direction of an intra-prediction mode. In other words, the value of the specified reference sample may be copied as the value of a pixel located in a direction reverse to the direction of the intra-prediction mode. Alternatively, the value of a pixel in the prediction block may be the value of a reference sample located in the direction of the intra-prediction mode with respect to the location of the pixel.

In an example, when the intra-prediction mode of a target block is a vertical mode having a mode value of 26, the above reference samples 837 may be used for intra prediction. When the intra-prediction mode is the vertical mode, the value of a pixel in the prediction block may be the value of a reference sample vertically located above the location of the pixel. Therefore, the above reference samples 837 adjacent to the top of the target block may be used for intra prediction. Furthermore, the values of pixels in one row of the prediction block may be identical to those of the above reference samples 837.

In an example, when the intra-prediction mode of a target block is a horizontal mode having a mode value of 10, the left reference samples 833 may be used for intra prediction. When the intra-prediction mode is the horizontal mode, the value of a pixel in the prediction block may be the value of a reference sample horizontally located left to the location of the pixel. Therefore, the left reference samples 833 adjacent to the left of the target block may be used for intra prediction. Furthermore, the values of pixels in one column of the prediction block may be identical to those of the left reference samples 833.

In an example, when the mode value of the intra-prediction mode of the current block is 18, at least some of the left reference samples 833, the above-left corner reference sample 835, and at least some of the above reference samples 837 may be used for intra prediction. When the mode value of the intra-prediction mode is 18, the value of a pixel in the prediction block may be the value of a reference sample diagonally located at the above-left corner of the pixel.

Further, At least a part of the above-right reference samples 839 may be used for intra prediction in a case that a intra prediction mode having a mode value of 27, 28, 29, 30, 31, 32, 33 or 34 is used.

Further, At least a part of the below-left reference samples 831 may be used for intra prediction in a case that a intra prediction mode having a mode value of 2, 3, 4, 5, 6, 7, 8 or 9 is used.

Further, the above-left corner reference sample 835 may be used for intra prediction in a case that a intra prediction mode of which a mode value is a value ranging from 11 to 25.

The number of reference samples used to determine the pixel value of one pixel in the prediction block may be either 1, or 2 or more.

As described above, the pixel value of a pixel in the prediction block may be determined depending on the location of the pixel and the location of a reference sample indicated by the direction of the intra-prediction mode. When the location of the pixel and the location of the reference sample indicated by the direction of the intra-prediction mode are integer positions, the value of one reference sample indicated by an integer position may be used to determine the pixel value of the pixel in the prediction block.

When the location of the pixel and the location of the reference sample indicated by the direction of the intra-prediction mode are not integer positions, an interpolated reference sample based on two reference samples closest to the location of the reference sample may be generated. The value of the interpolated reference sample may be used to determine the pixel value of the pixel in the prediction block. In other words, when the location of the pixel in the prediction block and the location of the reference sample indicated by the direction of the intra-prediction mode indicate the location between two reference samples, an interpolated value based on the values of the two samples may be generated.

The prediction block generated via prediction may not be identical to an original target block. In other words, there may be a prediction error which is the difference between the target block and the prediction block, and there may also be a prediction error between the pixel of the target block and the pixel of the prediction block.

Hereinafter, the terms “difference”, “error”, and “residual” may be used to have the same meaning, and may be used interchangeably with each other.

For example, in the case of directional intra prediction, the longer the distance between the pixel of the prediction block and the reference sample, the greater the prediction error that may occur. Such a prediction error may result in discontinuity between the generated prediction block and neighboring blocks.

In order to reduce the prediction error, filtering for the prediction block may be used. Filtering may be configured to adaptively apply a filter to an area, regarded as having a large prediction error, in the prediction block. For example, the area regarded as having a large prediction error may be the boundary of the prediction block. Further, an area regarded as having a large prediction error in the prediction block may differ depending on the intra-prediction mode, and the characteristics of filters may also differ depending thereon.

FIG. 9 is a diagram for explaining an embodiment of an inter prediction procedure.

The rectangles shown in FIG. 9 may represent images (or pictures). Further, in FIG. 9, arrows may represent prediction directions. That is, each image may be encoded and/or decoded depending on the prediction direction.

Images may be classified into an Intra Picture (I picture), a Uni-prediction Picture or Predictive Coded Picture (P picture), and a Bi-prediction Picture or Bi-predictive Coded Picture (B picture) depending on the encoding type. Each picture may be encoded and/or decoded depending on the encoding type thereof.

When a target image that is the target to be encoded is an I picture, the target image may be encoded using data contained in the image itself without inter prediction that refers to other images. For example, an I picture may be encoded only via intra prediction.

When a target image is a P picture, the target image may be encoded via inter prediction, which uses reference pictures existing in one direction. Here, the one direction may be a forward direction or a backward direction.

When a target image is a B picture, the image may be encoded via inter prediction that uses reference pictures existing in two directions, or may be encoded via inter prediction that uses reference pictures existing in one of a forward direction and a backward direction. Here, the two directions may be the forward direction and the backward direction.

A P picture and a B picture that are encoded and/or decoded using reference pictures may be regarded as images in which inter prediction is used.

Below, inter prediction in an inter mode according to an embodiment will be described in detail.

Inter prediction may be performed using motion information.

In an inter mode, the encoding apparatus 100 may perform inter prediction and/or motion compensation on a target block. The decoding apparatus 200 may perform inter prediction and/or motion compensation, corresponding to inter prediction and/or motion compensation performed by the encoding apparatus 100, on a target block.

Motion information of the target block may be individually derived by the encoding apparatus 100 and the decoding apparatus 200 during the inter prediction. The motion information may be derived using motion information of a reconstructed neighboring block, motion information of a col block, and/or motion information of a block adjacent to the col block.

For example, the encoding apparatus 100 or the decoding apparatus 200 may perform prediction and/or motion compensation by using motion information of a spatial candidate and/or a temporal candidate as motion information of the target block. The target block may mean a PU and/or a PU partition.

A spatial candidate may be a reconstructed block which is spatially adjacent to the target block.

A temporal candidate may be a reconstructed block corresponding to the target block in a previously reconstructed co-located picture (col picture).

In inter prediction, the encoding apparatus 100 and the decoding apparatus 200 may improve encoding efficiency and decoding efficiency by utilizing the motion information of a spatial candidate and/or a temporal candidate. The motion information of a spatial candidate may be referred to as ‘spatial motion information’. The motion information of a temporal candidate may be referred to as ‘temporal motion information’.

Below, the motion information of a spatial candidate may be the motion information of a PU including the spatial candidate. The motion information of a temporal candidate may be the motion information of a PU including the temporal candidate. The motion information of a candidate block may be the motion information of a PU including the candidate block.

Inter prediction may be performed using a reference picture.

The reference picture may be at least one of a picture previous to a target picture and a picture subsequent to the target picture. The reference picture may be an image used for the prediction of the target block.

In inter prediction, a region in the reference picture may be specified by utilizing a reference picture index (or refIdx) for indicating a reference picture, a motion vector, which will be described later, etc. Here, the region specified in the reference picture may indicate a reference block.

Inter prediction may select a reference picture, and may also select a reference block corresponding to the target block from the reference picture. Further, inter prediction may generate a prediction block for the target block using the selected reference block.

The motion information may be derived during inter prediction by each of the encoding apparatus 100 and the decoding apparatus 200.

A spatial candidate may be a block 1) which is present in a target picture, 2) which has been previously reconstructed via encoding and/or decoding, and 3) which is adjacent to the target block or is located at the corner of the target block. Here, the “block located at the corner of the target block” may be either a block vertically adjacent to a neighboring block that is horizontally adjacent to the target block, or a block horizontally adjacent to a neighboring block that is vertically adjacent to the target block. Further, “block located at the corner of the target block” may have the same meaning as “block adjacent to the corner of the target block”. The meaning of “block located at the corner of the target block” may be included in the meaning of “block adjacent to the target block”.

For example, a spatial candidate may be a reconstructed block located to the left of the target block, a reconstructed block located above the target block, a reconstructed block located at the below-left corner of the target block, a reconstructed block located at the above-right corner of the target block, or a reconstructed block located at the above-left corner of the target block.

Each of the encoding apparatus 100 and the decoding apparatus 200 may identify a block present at the location spatially corresponding to the target block in a col picture. The location of the target block in the target picture and the location of the identified block in the col picture may correspond to each other.

Each of the encoding apparatus 100 and the decoding apparatus 200 may determine a col block present at the predefined relative location for the identified block to be a temporal candidate. The predefined relative location may be a location present inside and/or outside the identified block.

For example, the col block may include a first col block and a second col block. When the coordinates of the identified block are (xP, yP) and the size of the identified block is represented by (nPSW, nPSH), the first col block may be a block located at coordinates (xP+nPSW, yP+nPSH). The second col block may be a block located at coordinates (xP+(nPSW>>1), yP+(nPSH>>1)). The second col block may be selectively used when the first col block is unavailable.

The motion vector of the target block may be determined based on the motion vector of the col block. Each of the encoding apparatus 100 and the decoding apparatus 200 may scale the motion vector of the col block. The scaled motion vector of the col block may be used as the motion vector of the target block. Further, a motion vector for the motion information of a temporal candidate stored in a list may be a scaled motion vector.

The ratio of the motion vector of the target block to the motion vector of the col block may be identical to the ratio of a first temporal distance to a second temporal distance. The first temporal distance may be the distance between the reference picture and the target picture of the target block. The second temporal distance may be the distance between the reference picture and the col picture of the col block.

The scheme for deriving motion information may change depending on the inter-prediction mode of a target block. For example, as inter-prediction modes applied for inter prediction, an Advanced Motion Vector Predictor (AMVP) mode, a merge mode, a skip mode, a current picture reference mode, etc. may be present. The merge mode may also be referred to as a “motion merge mode”. Individual modes will be described in detail below.

1) AMVP Mode

When an AMVP mode is used, the encoding apparatus 100 may search a neighboring region of a target block for a similar block. The encoding apparatus 100 may acquire a prediction block by performing prediction on the target block using motion information of the found similar block. The encoding apparatus 100 may encode a residual block, which is the difference between the target block and the prediction block.

1-1) Creation of List of Prediction Motion Vector Candidates

When an AMVP mode is used as the prediction mode, each of the encoding apparatus 100 and the decoding apparatus 200 may create a list of prediction motion vector candidates using the motion vector of a spatial candidate, the motion vector of a temporal candidate, and a zero vector. The prediction motion vector candidate list may include one or more prediction motion vector candidates. At least one of the motion vector of a spatial candidate, the motion vector of a temporal candidate, and a zero vector may be determined and used as a prediction motion vector candidate.

Hereinafter, the terms “prediction motion vector (candidate)” and “motion vector (candidate)” may be used to have the same meaning, and may be used interchangeably with each other.

Hereinafter, the terms “prediction motion vector candidate” and “AMVP candidate” may be used to have the same meaning, and may be used interchangeably with each other.

Hereinafter, the terms “prediction motion vector candidate list” and “AMVP candidate list” may be used to have the same meaning, and may be used interchangeably with each other.

Spatial candidates may include a reconstructed spatial neighboring block. In other words, the motion vector of the reconstructed neighboring block may be referred to as a “spatial prediction motion vector candidate”.

Temporal candidates may include a col block and a block adjacent to the col block. In other words, the motion vector of the col block or the motion vector of the block adjacent to the col block may be referred to as a “temporal prediction motion vector candidate”.

The zero vector may be a (0, 0) motion vector.

The prediction motion vector candidates may be motion vector predictors for predicting a motion vector. Also, in the encoding apparatus 100, each prediction motion vector candidate may be an initial search location for a motion vector.

1-2) Search for Motion Vectors that Use List of Prediction Motion Vector Candidates

The encoding apparatus 100 may determine the motion vector to be used to encode a target block within a search range using a list of prediction motion vector candidates. Further, the encoding apparatus 100 may determine a prediction motion vector candidate to be used as the prediction motion vector of the target block, among prediction motion vector candidates present in the prediction motion vector candidate list.

The motion vector to be used to encode the target block may be a motion vector that can be encoded at minimum cost.

Further, the encoding apparatus 100 may determine whether to use the AMVP mode to encode the target block.

1-3) Transmission of Inter-Prediction Information

The encoding apparatus 100 may generate a bitstream including inter-prediction information required for inter prediction. The decoding apparatus 200 may perform inter prediction on the target block using the inter-prediction information of the bitstream.

The inter-prediction information may contain 1) mode information indicating whether an AMVP mode is used, 2) a prediction motion vector index, 3) a Motion Vector Difference (MVD), 4) a reference direction, and 5) a reference picture index.

Hereinafter, the terms “prediction motion vector index” and “AMVP index” may be used to have the same meaning, and may be used interchangeably with each other.

Further, the inter-prediction information may contain a residual signal.

The decoding apparatus 200 may acquire a prediction motion vector index, an MVD, a reference direction, and a reference picture index from the bitstream through entropy decoding when mode information indicates that the AMVP mode is used.

The prediction motion vector index may indicate a prediction motion vector candidate to be used for the prediction of a target block, among prediction motion vector candidates included in the prediction motion vector candidate list.

1-4) Inter Prediction in AMVP Mode that Uses Inter-Prediction Information

The decoding apparatus 200 may derive prediction motion vector candidates using a prediction motion vector candidate list, and may determine the motion information of a target block based on the derived prediction motion vector candidates.

The decoding apparatus 200 may determine a motion vector candidate for the target block, among the prediction motion vector candidates included in the prediction motion vector candidate list, using a prediction motion vector index. The decoding apparatus 200 may select a prediction motion vector candidate, indicated by the prediction motion vector index, from among prediction motion vector candidates included in the prediction motion vector candidate list, as the prediction motion vector of the target block.

The motion vector to be actually used for inter prediction of the target block may not match the prediction motion vector. In order to indicate the difference between the motion vector to be actually used for inter prediction of the target block and the prediction motion vector, an MVD may be used. The encoding apparatus 100 may derive a prediction motion vector similar to the motion vector to be actually used for inter prediction of the target block so as to use an MVD that is as small as possible.

An MVD may be the difference between the motion vector of the target block and the prediction motion vector. The encoding apparatus 100 may calculate an MVD and may entropy-encode the MVD.

The MVD may be transmitted from the encoding apparatus 100 to the decoding apparatus 200 through a bitstream. The decoding apparatus 200 may decode the received MVD. The decoding apparatus 200 may derive the motion vector of the target block by summing the decoded MVD and the prediction motion vector. In other words, the motion vector of the target block derived by the decoding apparatus 200 may be the sum of the entropy-decoded MVD and the motion vector candidate.

The reference direction may indicate a list of reference pictures to be used for prediction of the target block. For example, the reference direction may indicate one of a reference picture list L0 and a reference picture list L1.

The reference direction merely indicates the reference picture list to be used for prediction of the target block, and may not mean that the directions of reference pictures are limited to a forward direction or a backward direction. In other words, each of the reference picture list L0 and the reference picture list L1 may include pictures in a forward direction and/or a backward direction.

That the reference direction is unidirectional may mean that a single reference picture list is used. That the reference direction is bidirectional may mean that two reference picture lists are used. In other words, the reference direction may indicate one of the case where only the reference picture list L0 is used, the case where only the reference picture list L1 is used, and the case where two reference picture lists are used.

The reference picture index may indicate a reference picture to be used for prediction of a target block, among reference pictures in the reference picture list. The reference picture index may be entropy-encoded by the encoding apparatus 100. The entropy-encoded reference picture index may be signaled to the decoding apparatus 200 by the encoding apparatus 100 through a bitstream.

When two reference picture lists are used to predict the target block, a single reference picture index and a single motion vector may be used for each of the reference picture lists. Further, when two reference picture lists are used to predict the target block, two prediction blocks may be specified for the target block. For example, the (final) prediction block of the target block may be generated using the average or weighted sum of the two prediction blocks for the target block.

The motion vector of the target block may be derived by the prediction motion vector index, the MVD, the reference direction, and the reference picture index.

The decoding apparatus 200 may generate a prediction block for the target block based on the derived motion vector and the reference picture index. For example, the prediction block may be a reference block, indicated by the derived motion vector, in the reference picture indicated by the reference picture index.

Since the prediction motion vector index and the MVD are encoded without the motion vector itself of the target block being encoded, the number of bits transmitted from the encoding apparatus 100 to the decoding apparatus 200 may be decreased, and encoding efficiency may be improved.

For the target block, the motion information of reconstructed neighboring blocks may be used. In a specific inter-prediction mode, the encoding apparatus 100 may not separately encode the actual motion information of the target block. The motion information of the target block is not encoded, and additional information that enables the motion information of the target block to be derived using the motion information of reconstructed neighboring blocks may be encoded instead. As the additional information is encoded, the number of bits transmitted to the decoding apparatus 200 may be decreased, and encoding efficiency may be improved.

For example, as inter-prediction modes in which the motion information of the target block is not directly encoded, there may be a skip mode and/or a merge mode. Here, each of the encoding apparatus 100 and the decoding apparatus 200 may use an identifier and/or an index that indicates a unit, the motion information of which is to be used as the motion information of the target unit, among reconstructed neighboring units.

2) Merge Mode

As a scheme for deriving the motion information of a target block, there is merging. The term “merging” may mean the merging of the motion of multiple blocks. “Merging” may mean that the motion information of one block is also applied to other blocks. In other words, a merge mode may be a mode in which the motion information of the target block is derived from the motion information of a neighboring block.

When a merge mode is used, the encoding apparatus 100 may predict the motion information of a target block using the motion information of a spatial candidate and/or the motion information of a temporal candidate. The spatial candidate may include a reconstructed spatial neighboring block that is spatially adjacent to the target block. The spatial neighboring block may include a left adjacent block and an above adjacent block. The temporal candidate may include a col block. The terms “spatial candidate” and “spatial merge candidate” may be used to have the same meaning, and may be used interchangeably with each other. The terms “temporal candidate” and “temporal merge candidate” may be used to have the same meaning, and may be used interchangeably with each other.

The encoding apparatus 100 may acquire a prediction block via prediction. The encoding apparatus 100 may encode a residual block, which is the difference between the target block and the prediction block.

2-1) Creation of Merge Candidate List

When the merge mode is used, each of the encoding apparatus 100 and the decoding apparatus 200 may create a merge candidate list using the motion information of a spatial candidate and/or the motion information of a temporal candidate. The motion information may include 1) a motion vector, 2) a reference picture index, and 3) a reference direction. The reference direction may be unidirectional or bidirectional.

The merge candidate list may include merge candidates. The merge candidates may be motion information. In other words, the merge candidate list may be a list in which pieces of motion information are stored.

The merge candidates may be pieces of motion information of temporal candidates and/or spatial candidates. Further, the merge candidate list may include new merge candidates generated by a combination of merge candidates that are already present in the merge candidate list. In other words, the merge candidate list may include new motion information generated by a combination of pieces of motion information previously present in the merge candidate list.

The merge candidates may be specific modes deriving inter prediction information. The merge candidate may be information indicating a specific mode deriving inter prediction information. Inter prediction information of a target block may be derived according to a specific mode which the merge candidate indicates. Furthermore, the specific mode may include a process of deriving a series of inter prediction information. This specific mode may be an inter prediction information derivation mode or a motion information derivation mode.

The inter prediction information of the target block may be derived according to the mode indicated by the merge candidate selected by the merge index among the merge candidates in the merge candidate list.

For example, the motion information derivation modes in the merge candidate list may be at least one of 1) motion information derivation mode for a sub-block unit and 2) an affine motion information derivation mode.

Furthermore, the merge candidate list may include motion information of a zero vector. The zero vector may also be referred to as a “zero-merge candidate”.

In other words, pieces of motion information in the merge candidate list may be at least one of 1) motion information of a spatial candidate, 2) motion information of a temporal candidate, 3) motion information generated by a combination of pieces of motion information previously present in the merge candidate list, and 4) a zero vector.

Motion information may include 1) a motion vector, 2) a reference picture index, and 3) a reference direction. The reference direction may also be referred to as an “inter-prediction indicator”. The reference direction may be unidirectional or bidirectional. The unidirectional reference direction may indicate L0 prediction or L1 prediction.

The merge candidate list may be created before prediction in the merge mode is performed.

The number of merge candidates in the merge candidate list may be predefined. Each of the encoding apparatus 100 and the decoding apparatus 200 may add merge candidates to the merge candidate list depending on the predefined scheme and predefined priorities so that the merge candidate list has a predefined number of merge candidates. The merge candidate list of the encoding apparatus 100 and the merge candidate list of the decoding apparatus 200 may be made identical to each other using the predefined scheme and the predefined priorities.

Merging may be applied on a CU basis or a PU basis. When merging is performed on a CU basis or a PU basis, the encoding apparatus 100 may transmit a bitstream including predefined information to the decoding apparatus 200. For example, the predefined information may contain 1) information indicating whether to perform merging for individual block partitions, and 2) information about a block with which merging is to be performed, among blocks that are spatial candidates and/or temporal candidates for the target block.

2-2) Search for Motion Vector that Uses Merge Candidate List

The encoding apparatus 100 may determine merge candidates to be used to encode a target block. For example, the encoding apparatus 100 may perform prediction on the target block using merge candidates in the merge candidate list, and may generate residual blocks for the merge candidates. The encoding apparatus 100 may use a merge candidate that incurs the minimum cost in prediction and in the encoding of residual blocks to encode the target block.

Further, the encoding apparatus 100 may determine whether to use a merge mode to encode the target block.

2-3) Transmission of Inter-Prediction Information

The encoding apparatus 100 may generate a bitstream that includes inter-prediction information required for inter prediction. The encoding apparatus 100 may generate entropy-encoded inter-prediction information by performing entropy encoding on inter-prediction information, and may transmit a bitstream including the entropy-encoded inter-prediction information to the decoding apparatus 200. Through the bitstream, the entropy-encoded inter-prediction information may be signaled to the decoding apparatus 200 by the encoding apparatus 100.

The decoding apparatus 200 may perform inter prediction on the target block using the inter-prediction information of the bitstream.

The inter-prediction information may contain 1) mode information indicating whether a merge mode is used and 2) a merge index.

Further, the inter-prediction information may contain a residual signal.

The decoding apparatus 200 may acquire the merge index from the bitstream only when the mode information indicates that the merge mode is used.

The mode information may be a merge flag. The unit of the mode information may be a block. Information about the block may include mode information, and the mode information may indicate whether a merge mode is applied to the block.

The merge index may indicate a merge candidate to be used for the prediction of the target block, among merge candidates included in the merge candidate list. Alternatively, the merge index may indicate a block with which the target block is to be merged, among neighboring blocks spatially or temporally adjacent to the target block.

The encoding apparatus 100 may select a merge candidate having the highest encoding performance among the merge candidates included in the merge candidate list and set a value of the merge index to indicate the selected merge candidate.

2-4) Inter Prediction of Merge Mode that Uses Inter-Prediction Information

The decoding apparatus 200 may perform prediction on the target block using the merge candidate indicated by the merge index, among merge candidates included in the merge candidate list.

The motion vector of the target block may be specified by the motion vector, reference picture index, and reference direction of the merge candidate indicated by the merge index.

3) Skip Mode

A skip mode may be a mode in which the motion information of a spatial candidate or the motion information of a temporal candidate is applied to the target block without change. Also, the skip mode may be a mode in which a residual signal is not used. In other words, when the skip mode is used, a reconstructed block may be a prediction block.

The difference between the merge mode and the skip mode lies in whether or not a residual signal is transmitted or used. That is, the skip mode may be similar to the merge mode except that a residual signal is not transmitted or used.

When the skip mode is used, the encoding apparatus 100 may transmit information about a block, the motion information of which is to be used as the motion information of the target block, among blocks that are spatial candidates or temporal candidates, to the decoding apparatus 200 through a bitstream. The encoding apparatus 100 may generate entropy-encoded information by performing entropy encoding on the information, and may signal the entropy-encoded information to the decoding apparatus 200 through a bitstream.

Further, when the skip mode is used, the encoding apparatus 100 may not transmit other syntax information, such as an MVD, to the decoding apparatus 200. For example, when the skip mode is used, the encoding apparatus 100 may not signal a syntax element related to at least one of an MVD, a coded block flag, and a transform coefficient level to the decoding apparatus 200.

3-1) Creation of Merge Candidate List

The skip mode may also use a merge candidate list. In other words, a merge candidate list may be used both in the merge mode and in the skip mode. In this aspect, the merge candidate list may also be referred to as a “skip candidate list” or a “merge/skip candidate list”.

Alternatively, the skip mode may use an additional candidate list different from that of the merge mode. In this case, in the following description, a merge candidate list and a merge candidate may be replaced with a skip candidate list and a skip candidate, respectively.

The merge candidate list may be created before prediction in the skip mode is performed.

3-2) Search for Motion Vector that Uses Merge Candidate List

The encoding apparatus 100 may determine the merge candidates to be used to encode a target block. For example, the encoding apparatus 100 may perform prediction on the target block using the merge candidates in a merge candidate list. The encoding apparatus 100 may use a merge candidate that incurs the minimum cost in prediction to encode the target block.

Further, the encoding apparatus 100 may determine whether to use a skip mode to encode the target block.

3-3) Transmission of Inter-Prediction Information

The encoding apparatus 100 may generate a bitstream that includes inter-prediction information required for inter prediction. The decoding apparatus 200 may perform inter prediction on the target block using the inter-prediction information of the bitstream.

The inter-prediction information may include 1) mode information indicating whether a skip mode is used, and 2) a skip index.

The skip index may be identical to the above-described merge index.

When the skip mode is used, the target block may be encoded without using a residual signal. The inter-prediction information may not contain a residual signal. Alternatively, the bitstream may not include a residual signal.

The decoding apparatus 200 may acquire a skip index from the bitstream only when the mode information indicates that the skip mode is used. As described above, a merge index and a skip index may be identical to each other. The decoding apparatus 200 may acquire the skip index from the bitstream only when the mode information indicates that the merge mode or the skip mode is used.

The skip index may indicate the merge candidate to be used for the prediction of the target block, among the merge candidates included in the merge candidate list.

3-4) Inter Prediction in Skip Mode that Uses Inter-Prediction Information

The decoding apparatus 200 may perform prediction on the target block using a merge candidate indicated by a skip index, among the merge candidates included in a merge candidate list.

The motion vector of the target block may be specified by the motion vector, reference picture index, and reference direction of the merge candidate indicated by the skip index.

4) Current Picture Reference Mode

The current picture reference mode may denote a prediction mode that uses a previously reconstructed region in a target picture to which a target block belongs.

A motion vector for specifying the previously reconstructed region may be used. Whether the target block has been encoded in the current picture reference mode may be determined using the reference picture index of the target block.

A flag or index indicating whether the target block is a block encoded in the current picture reference mode may be signaled by the encoding apparatus 100 to the decoding apparatus 200. Alternatively, whether the target block is a block encoded in the current picture reference mode may be inferred through the reference picture index of the target block.

When the target block is encoded in the current picture reference mode, the target picture may exist at a fixed location or an arbitrary location in a reference picture list for the target block.

For example, the fixed location may be either a location where a value of the reference picture index is 0 or the last location.

When the target picture exists at an arbitrary location in the reference picture list, an additional reference picture index indicating such an arbitrary location may be signaled by the encoding apparatus 100 to the decoding apparatus 200.

In the above-described AMVP mode, merge mode, and skip mode, motion information to be used for the prediction of a target block may be specified, among pieces of motion information in the list, using the index of the list.

In order to improve encoding efficiency, the encoding apparatus 100 may signal only the index of an element that incurs the minimum cost in inter prediction of the target block, among elements in the list. The encoding apparatus 100 may encode the index, and may signal the encoded index.

Therefore, the above-described lists (i.e. the prediction motion vector candidate list and the merge candidate list) must be able to be derived by the encoding apparatus 100 and the decoding apparatus 200 using the same scheme based on the same data. Here, the same data may include a reconstructed picture and a reconstructed block. Further, in order to specify an element using an index, the order of the elements in the list must be fixed.

FIG. 10 illustrates spatial candidates according to an embodiment.

In FIG. 10, the locations of spatial candidates are illustrated.

The large block in the center of the drawing may denote a target block. Five small blocks may denote spatial candidates.

The coordinates of the target block may be (xP, yP), and the size of the target block may be represented by (nPSW, nPSH).

Spatial candidate A₀ may be a block adjacent to the below-left corner of the target block. A₀ may be a block that occupies pixels located at coordinates (xP−1, yP+nPSH+1).

Spatial candidate A₁ may be a block adjacent to the left of the target block. A₁ may be a lowermost block, among blocks adjacent to the left of the target block. Alternatively, A₁ may be a block adjacent to the top of A₀. A₁ may be a block that occupies pixels located at coordinates (xP−1, yP+nPSH).

Spatial candidate B₀ may be a block adjacent to the above-right corner of the target block. B₀ may be a block that occupies pixels located at coordinates (xP+nPSW+1, yP−1).

Spatial candidate B₁ may be a block adjacent to the top of the target block. B₁ may be a rightmost block, among blocks adjacent to the top of the target block. Alternatively, B₁ may be a block adjacent to the left of B₀. B₁ may be a block that occupies pixels located at coordinates (xP+nPSW, yP−1).

Spatial candidate B₂ may be a block adjacent to the above-left corner of the target block. B₂ may be a block that occupies pixels located at coordinates (xP−1, yP−1).

Determination of Availability of Spatial Candidate and Temporal Candidate

In order to include the motion information of a spatial candidate or the motion information of a temporal candidate in a list, it must be determined whether the motion information of the spatial candidate or the motion information of the temporal candidate is available.

Hereinafter, a candidate block may include a spatial candidate and a temporal candidate.

For example, the determination may be performed by sequentially applying the following steps 1) to 4).

Step 1) When a PU including a candidate block is out of the boundary of a picture, the availability of the candidate block may be set to “false”. The expression “availability is set to false” may have the same meaning as “set to be unavailable”.

Step 2) When a PU including a candidate block is out of the boundary of a slice, the availability of the candidate block may be set to “false”. When the target block and the candidate block are located in different slices, the availability of the candidate block may be set to “false”.

Step 3) When a PU including a candidate block is out of the boundary of a tile, the availability of the candidate block may be set to “false”. When the target block and the candidate block are located in different tiles, the availability of the candidate block may be set to “false”.

Step 4) When the prediction mode of a PU including a candidate block is an intra-prediction mode, the availability of the candidate block may be set to “false”. When a PU including a candidate block does not use inter prediction, the availability of the candidate block may be set to “false”.

FIG. 11 illustrates the order of addition of motion information of spatial candidates to a merge list according to an embodiment.

As shown in FIG. 11, when pieces of motion information of spatial candidates are added to a merge list, the order of A₁, B₁, B₀, A₀, and B₂ may be used. That is, pieces of motion information of available spatial candidates may be added to the merge list in the order of A₁, B₁, B₀, A₀, and B₂.

Method for Deriving Merge List in Merge Mode and Skip Mode

As described above, the maximum number of merge candidates in the merge list may be set. The set maximum number is indicated by “N”. The set number may be transmitted from the encoding apparatus 100 to the decoding apparatus 200. The slice header of a slice may include N. In other words, the maximum number of merge candidates in the merge list for the target block of the slice may be set by the slice header. For example, the value of N may be basically 5.

Pieces of motion information (i.e., merge candidates) may be added to the merge list in the order of the following steps 1) to 4).

Step 1) Among spatial candidates, available spatial candidates may be added to the merge list. Pieces of motion information of the available spatial candidates may be added to the merge list in the order illustrated in FIG. 10. Here, when the motion information of an available spatial candidate overlaps other motion information already present in the merge list, the motion information may not be added to the merge list. The operation of checking whether the corresponding motion information overlaps other motion information present in the list may be referred to in brief as an “overlap check”.

The maximum number of pieces of motion information that are added may be N.

Step 2) When the number of pieces of motion information in the merge list is less than N and a temporal candidate is available, the motion information of the temporal candidate may be added to the merge list. Here, when the motion information of the available temporal candidate overlaps other motion information already present in the merge list, the motion information may not be added to the merge list.

Step 3) When the number of pieces of motion information in the merge list is less than N and the type of a target slice is “B”, combined motion information generated by combined bidirectional prediction (bi-prediction) may be added to the merge list.

The target slice may be a slice including a target block.

The combined motion information may be a combination of L0 motion information and L1 motion information. L0 motion information may be motion information that refers only to a reference picture list L0. L1 motion information may be motion information that refers only to a reference picture list L1.

In the merge list, one or more pieces of L0 motion information may be present. Further, in the merge list, one or more pieces of L1 motion information may be present.

The combined motion information may include one or more pieces of combined motion information. When the combined motion information is generated, L0 motion information and L1 motion information, which are to be used for generation, among the one or more pieces of L0 motion information and the one or more pieces of L1 motion information, may be predefined. One or more pieces of combined motion information may be generated in a predefined order via combined bidirectional prediction, which uses a pair of different pieces of motion information in the merge list. One of the pair of different pieces of motion information may be L0 motion information and the other of the pair may be L1 motion information.

For example, combined motion information that is added with the highest priority may be a combination of L0 motion information having a merge index of 0 and L1 motion information having a merge index of 1. When motion information having a merge index of 0 is not L0 motion information or when motion information having a merge index of 1 is not L1 motion information, the combined motion information may be neither generated nor added. Next, the combined motion information that is added with the next priority may be a combination of L0 motion information, having a merge index of 1, and L1 motion information, having a merge index of 0. Subsequent detailed combinations may conform to other combinations of video encoding/decoding fields.

Here, when the combined motion information overlaps other motion information already present in the merge list, the combined motion information may not be added to the merge list.

Step 4) When the number of pieces of motion information in the merge list is less than N, motion information of a zero vector may be added to the merge list.

The zero-vector motion information may be motion information for which the motion vector is a zero vector.

The number of pieces of zero-vector motion information may be one or more. The reference picture indices of one or more pieces of zero-vector motion information may be different from each other. For example, the value of the reference picture index of first zero-vector motion information may be 0. The value of the reference picture index of second zero-vector motion information may be 1.

The number of pieces of zero-vector motion information may be identical to the number of reference pictures in the reference picture list.

The reference direction of zero-vector motion information may be bidirectional. Both of the motion vectors may be zero vectors. The number of pieces of zero-vector motion information may be the smaller one of the number of reference pictures in the reference picture list L0 and the number of reference pictures in the reference picture list L1. Alternatively, when the number of reference pictures in the reference picture list L0 and the number of reference pictures in the reference picture list L1 are different from each other, a reference direction that is unidirectional may be used for a reference picture index that may be applied only to a single reference picture list.

The encoding apparatus 100 and/or the decoding apparatus 200 may sequentially add the zero-vector motion information to the merge list while changing the reference picture index.

When zero-vector motion information overlaps other motion information already present in the merge list, the zero-vector motion information may not be added to the merge list.

The order of the above-described steps 1) to 4) is merely exemplary, and may be changed. Further, some of the above steps may be omitted depending on predefined conditions.

Method for Deriving Prediction Motion Vector Candidate List in AMVP Mode

The maximum number of prediction motion vector candidates in a prediction motion vector candidate list may be predefined. The predefined maximum number is indicated by N. For example, the predefined maximum number may be 2.

Pieces of motion information (i.e. prediction motion vector candidates) may be added to the prediction motion vector candidate list in the order of the following steps 1) to 3).

Step 1) Available spatial candidates, among spatial candidates, may be added to the prediction motion vector candidate list. The spatial candidates may include a first spatial candidate and a second spatial candidate.

The first spatial candidate may be one of A₀, A₁, scaled A₀, and scaled A₁. The second spatial candidate may be one of B₀, B₁, B₂, scaled B₀, scaled B₁, and scaled B₂.

Pieces of motion information of available spatial candidates may be added to the prediction motion vector candidate list in the order of the first spatial candidate and the second spatial candidate. In this case, when the motion information of an available spatial candidate overlaps other motion information already present in the prediction motion vector candidate list, the motion information may not be added to the prediction motion vector candidate list. In other words, when the value of N is 2, if the motion information of a second spatial candidate is identical to the motion information of a first spatial candidate, the motion information of the second spatial candidate may not be added to the prediction motion vector candidate list.

The maximum number of pieces of motion information that are added may be N.

Step 2) When the number of pieces of motion information in the prediction motion vector candidate list is less than N and a temporal candidate is available, the motion information of the temporal candidate may be added to the prediction motion vector candidate list. In this case, when the motion information of the available temporal candidate overlaps other motion information already present in the prediction motion vector candidate list, the motion information may not be added to the prediction motion vector candidate list.

Step 3) When the number of pieces of motion information in the prediction motion vector candidate list is less than N, zero-vector motion information may be added to the prediction motion vector candidate list.

The zero-vector motion information may include one or more pieces of zero-vector motion information. The reference picture indices of the one or more pieces of zero-vector motion information may be different from each other.

The encoding apparatus 100 and/or the decoding apparatus 200 may sequentially add pieces of zero-vector motion information to the prediction motion vector candidate list while changing the reference picture index.

When zero-vector motion information overlaps other motion information already present in the prediction motion vector candidate list, the zero-vector motion information may not be added to the prediction motion vector candidate list.

The description of the zero-vector motion information, made above in connection with the merge list, may also be applied to zero-vector motion information. A repeated description thereof will be omitted.

The order of the above-described steps 1) to 3) is merely exemplary, and may be changed. Further, some of the steps may be omitted depending on predefined conditions.

FIG. 12 illustrates a transform and quantization process according to an example.

As illustrated in FIG. 12, quantized levels may be generated by performing a transform and/or quantization process on a residual signal.

A residual signal may be generated as the difference between an original block and a prediction block. Here, the prediction block may be a block generated via intra prediction or inter prediction.

The residual signal may be transformed into a signal in a frequency domain through a transform procedure that is a part of a quantization procedure.

A transform kernel used for a transform may include various DCT kernels, such as Discrete Cosine Transform (DCT) type 2 (DCT-II) and Discrete Sine Transform (DST) kernels.

These transform kernels may perform a separable transform or a two-dimensional (2D) non-separable transform on the residual signal. The separable transform may be a transform indicating that a one-dimensional (1D) transform is performed on the residual signal in each of a horizontal direction and a vertical direction.

The DCT type and the DST type, which are adaptively used for a 1D transform, may include DCT-V, DCT-VIII, DST-I, and DST-VII in addition to DCT-II, as shown in each of the following Table 3 and the following table 4.

TABLE 3 Transform set Transform candidates 0 DST-VII, DCT-VIII 1 DST-VII, DST-I 2 DST-VII, DCT-V

TABLE 4 Transform set Transform candidates 0 DST-VII, DCT-VIII, DST-I 1 DST-VII, DST-I, DCT-VIII 2 DST-VII, DCT-V, DST-I

As shown in Table 3 and Table 4, when a DCT type or a DST type to be used for a transform is derived, transform sets may be used. Each transform set may include multiple transform candidates. Each transform candidate may be a DCT type or a DST type.

The following Table 5 shows examples of a transform set to be applied to a horizontal direction and a transform set to be applied to a vertical direction depending on intra-prediction modes.

TABLE 5 Intra-prediction mode 0 1 2 3 4 5 6 7 8 9 Vertical transform set 2 1 0 1 0 1 0 1 0 1 Horizontal transform set 2 1 0 1 0 1 0 1 0 1 Intra-prediction mode 10 11 12 13 14 15 16 17 18 19 Vertical transform set 0 1 0 1 0 0 0 0 0 0 Horizontal transform set 0 1 0 1 2 2 2 2 2 2 Intra-prediction mode 20 21 22 23 24 25 26 27 28 29 Vertical transform set 0 0 0 1 0 1 0 1 0 1 Horizontal transform set 2 2 2 1 0 1 0 1 0 1 Intra-prediction mode 30 31 32 33 34 35 36 37 38 39 Vertical transform set 0 1 0 1 0 1 0 1 0 1 Horizontal transform set 0 1 0 1 0 1 0 1 0 1 Intra-prediction mode 40 41 42 43 44 45 46 47 48 49 Vertical transform set 0 1 0 1 0 1 2 2 2 2 Horizontal transform set 0 1 0 1 0 1 0 0 0 0 Intra-prediction mode 50 51 52 53 54 55 56 57 58 59 Vertical transform set 2 2 2 2 2 1 0 1 0 1 Horizontal transform set 0 0 0 0 0 1 0 1 0 1 Intra-prediction mode 60 61 62 63 64 65 66 Vertical transform set 0 1 0 1 0 1 0 Horizontal transform set 0 1 0 1 0 1 0

In Table 5, numbers of vertical transform sets and horizontal transform sets that are to be applied to the horizontal direction of a residual signal depending on the intra-prediction modes of the target block are indicated.

As exemplified in FIGS. 4 and 5, transform sets to be applied to the horizontal direction and the vertical direction may be predefined depending on the intra-prediction mode of the target block. The encoding apparatus 100 may perform a transform and an inverse transform on the residual signal using a transform included in the transform set corresponding to the intra-prediction mode of the target block. Further, the decoding apparatus 200 may perform an inverse transform on the residual signal using a transform included in the transform set corresponding to the intra-prediction mode of the target block.

In the transform and inverse transform, transform sets to be applied to the residual signal may be determined, as exemplified in Tables 3, and 4, and may not be signaled. Transform indication information may be signaled from the encoding apparatus 100 to the decoding apparatus 200. The transform indication information may be information indicating which one of multiple transform candidates included in the transform set to be applied to the residual signal is used.

For example, when the size of the target block is 64×64 or less, transform sets, each having three transforms, may be configured depending on the intra-prediction modes, as shown in the examples of Table 4. An optimal transform method may be selected from among a total of nine multiple transform methods resulting from combinations of three transforms in a horizontal direction and three transforms in a vertical direction. Through such an optimal transform method, the residual signal may be encoded and/or decoded, and thus coding efficiency may be improved.

Here, information indicating which one of transforms belonging to each transform set has been used for at least one of a vertical transform and a horizontal transform may be entropy-encoded and/or -decoded. Here, truncated unary binarization may be used to encode and/or decode such information.

As described above, methods using various transforms may be applied to a residual signal generated via intra prediction or inter prediction.

The transform may include at least one of a first transform and a secondary transform. A transform coefficient may be generated by performing the first transform on the residual signal, and a secondary transform coefficient may be generated by performing the secondary transform on the transform coefficient.

The first transform may be referred to as a “primary transform”. Further, the first transform may also be referred to as an “Adaptive Multiple Transform (AMT) scheme”. AMT may mean that, as described above, different transforms are applied to respective 1D directions (i.e. a vertical direction and a horizontal direction).

A secondary transform may be a transform for improving energy concentration on a transform coefficient generated by the first transform. Similar to the first transform, the secondary transform may be a separable transform or a non-separable transform. Such a non-separable transform may be a Non-Separable Secondary Transform (NSST).

The first transform may be performed using at least one of predefined multiple transform methods. For example, the predefined multiple transform methods may include a Discrete Cosine Transform (DCT), a Discrete Sine Transform (DST), a Karhunen-Loeve Transform (KLT), etc.

Further, a first transform may be a transform having various types depending on a kernel function that defines a Discrete Cosine Transform (DCT) or a Discrete Sine Transform (DST).

For example, the first transform may include transforms, such as DCT-2, DCT-5, DCT-7, DST-1, and DST-8 depending on the transform kernel presented in the following Table 6. In the following Table 6, various transform types and transform kernel functions for Multiple Transform Selection (MTS) are exemplified.

MTS may refer to the selection of combinations of one or more DCT and/or DST kernels so as to transform a residual signal in a horizontal and/or vertical direction.

TABLE 6 Transform type Transform kernel function T_(i)(j) DCT-2 ${T_{i}(j)} = {\omega_{0} \cdot \sqrt{\frac{2}{N}} \cdot {\cos\left( \frac{\pi \cdot i \cdot \left( {{2j} + 1} \right)}{2N} \right)}}$ where $\omega_{0} = {\sqrt{\frac{2}{N}}\left( {i = 0} \right){or}1({otherwise})}$ DST-7 ${T_{i}(j)} = {\sqrt{\frac{4}{{2N} + 1}} \cdot {\sin\left( \frac{\pi \cdot \left( {{2j} + 1} \right) \cdot \left( {j + 1} \right)}{{2N} + 1} \right)}}$ DCT-5 ${T_{i}(j)} = {\omega_{0} \cdot \omega_{1} \cdot \sqrt{\frac{2}{{2N} - 1}} \cdot {\cos\left( \frac{2{\pi \cdot i \cdot j}}{{2N} + 1} \right)}}$ where $\omega_{0/1} = {\sqrt{\frac{2}{N}}\left( {{i{or}j} = 0} \right){or}1({otherwise})}$ DCT-8 ${T_{i}(j)} = {\sqrt{\frac{4}{{2N} + 1}} \cdot {\cos\left( \frac{\pi \cdot \left( {{2j} + 1} \right) \cdot \left( {{2j} + 1} \right)}{{4N} + 2} \right)}}$ DST-1 ${T_{i}(j)} = {\sqrt{\frac{2}{N + 1}} \cdot {\sin\left( \frac{\pi \cdot \left( {i + 1} \right) \cdot \left( {j + 1} \right)}{N + 1} \right)}}$

In Table 6, i and j may be integer values that are equal to or greater than 0 and are less than or equal to N−1.

The secondary transform may be performed on the transform coefficient generated by performing the first transform.

As in the first transform, transform sets may also be defined in a secondary transform. The methods for deriving and/or determining the above-described transform sets may be applied not only to the first transform but also to the secondary transform.

The first transform and the secondary transform may be determined for a specific target.

For example, a first transform and a secondary transform may be applied to signal components corresponding to one or more of a luminance (luma) component and a chrominance (chroma) component. Whether to apply the first transform and/or the secondary transform may be determined depending on at least one of coding parameters for a target block and/or a neighboring block. For example, whether to apply the first transform and/or the secondary transform may be determined depending on the size and/or shape of the target block.

In the encoding apparatus 100 and the decoding apparatus 200, transform information indicating the transform method to be used for the target may be derived by utilizing specified information.

For example, the transform information may include a transform index to be used for a primary transform and/or a secondary transform. Alternatively, the transform information may indicate that a primary transform and/or a secondary transform are not used.

For example, when the target of a primary transform and a secondary transform is a target block, the transform method(s) to be applied to the primary transform and/or the secondary transform indicated by the transform information may be determined depending on at least one of coding parameters for the target block and/or blocks neighboring the target block.

Alternatively, transform information for a specific target may be signaled from the encoding apparatus 100 to the decoding apparatus 200.

For example, for a single CU, whether to use a primary transform, an index indicating the primary transform, whether to use a secondary transform, and an index indicating the secondary transform may be derived as the transform information by the decoding apparatus 200. Alternatively, for a single CU, the transform information, which indicates whether to use a primary transform, an index indicating the primary transform, whether to use a secondary transform, and an index indicating the secondary transform, may be signaled.

The quantized transform coefficient (i.e. the quantized levels) may be generated by performing quantization on the result, generated by performing the first transform and/or the secondary transform, or on the residual signal.

FIG. 13 illustrates diagonal scanning according to an example.

FIG. 14 illustrates horizontal scanning according to an example.

FIG. 15 illustrates vertical scanning according to an example.

Quantized transform coefficients may be scanned via at least one of (up-right) diagonal scanning, vertical scanning, and horizontal scanning depending on at least one of an intra-prediction mode, a block size, and a block shape. The block may be a Transform Unit (TU).

Each scanning may be initiated at a specific start point, and may be terminated at a specific end point.

For example, quantized transform coefficients may be changed to 1D vector forms by scanning the coefficients of a block using diagonal scanning of FIG. 13. Alternatively, horizontal scanning of FIG. 14 or vertical scanning of FIG. 15, instead of diagonal scanning, may be used depending on the size and/or intra-prediction mode of a block.

Vertical scanning may be the operation of scanning 2D block-type coefficients in a column direction. Horizontal scanning may be the operation of scanning 2D block-type coefficients in a row direction.

In other words, which one of diagonal scanning, vertical scanning, and horizontal scanning is to be used may be determined depending on the size and/or inter-prediction mode of the block.

As illustrated in FIGS. 13, 14, and 15, the quantized transform coefficients may be scanned along a diagonal direction, a horizontal direction or a vertical direction.

The quantized transform coefficients may be represented by block shapes. Each block may include multiple sub-blocks. Each sub-block may be defined depending on a minimum block size or a minimum block shape.

In scanning, a scanning sequence depending on the type or direction of scanning may be primarily applied to sub-blocks. Further, a scanning sequence depending on the direction of scanning may be applied to quantized transform coefficients in each sub-block.

For example, as illustrated in FIGS. 13, 14, and 15, when the size of a target block is 8×8, quantized transform coefficients may be generated through a first transform, a secondary transform, and quantization on the residual signal of the target block. Therefore, one of three types of scanning sequences may be applied to four 4×4 sub-blocks, and quantized transform coefficients may also be scanned for each 4×4 sub-block depending on the scanning sequence.

The scanned quantized transform coefficients may be entropy-encoded, and a bitstream may include the entropy-encoded quantized transform coefficients.

The decoding apparatus 200 may generate quantized transform coefficients via entropy decoding on the bitstream. The quantized transform coefficients may be aligned in the form of a 2D block via inverse scanning Here, as the method of inverse scanning, at least one of up-right diagonal scanning, vertical scanning, and horizontal scanning may be performed.

In the decoding apparatus 200, dequantization may be performed on the quantized transform coefficients. A secondary inverse transform may be performed on the result generated by performing dequantization depending on whether to perform the secondary inverse transform. Further, a first inverse transform may be performed on the result generated by performing the secondary inverse transform depending on whether the first inverse transform is to be performed. A reconstructed residual signal may be generated by performing the first inverse transform on the result generated by performing the secondary inverse transform.

FIG. 16 is a configuration diagram of an encoding apparatus according to an embodiment.

An encoding apparatus 1600 may correspond to the above-described encoding apparatus 100.

The encoding apparatus 1600 may include a processing unit 1610, memory 1630, a user interface (UI) input device 1650, a UI output device 1660, and storage 1640, which communicate with each other through a bus 1690. The encoding apparatus 1600 may further include a communication unit 1620 coupled to a network 1699.

The processing unit 1610 may be a Central Processing Unit (CPU) or a semiconductor device for executing processing instructions stored in the memory 1630 or the storage 1640. The processing unit 1610 may be at least one hardware processor.

The processing unit 1610 may generate and process signals, data or information that are input to the encoding apparatus 1600, are output from the encoding apparatus 1600, or are used in the encoding apparatus 1600, and may perform examination, comparison, determination, etc. related to the signals, data or information. In other words, in embodiments, the generation and processing of data or information and examination, comparison and determination related to data or information may be performed by the processing unit 1610.

The processing unit 1610 may include an inter-prediction unit 110, an intra-prediction unit 120, a switch 115, a subtractor 125, a transform unit 130, a quantization unit 140, an entropy encoding unit 150, a dequantization unit 160, an inverse transform unit 170, an adder 175, a filter unit 180, and a reference picture buffer 190.

At least some of the inter-prediction unit 110, the intra-prediction unit 120, the switch 115, the subtractor 125, the transform unit 130, the quantization unit 140, the entropy encoding unit 150, the dequantization unit 160, the inverse transform unit 170, the adder 175, the filter unit 180, and the reference picture buffer 190 may be program modules, and may communicate with an external device or system. The program modules may be included in the encoding apparatus 1600 in the form of an operating system, an application program module, or other program modules.

The program modules may be physically stored in various types of well-known storage devices. Further, at least some of the program modules may also be stored in a remote storage device that is capable of communicating with the encoding apparatus 1200.

The program modules may include, but are not limited to, a routine, a subroutine, a program, an object, a component, and a data structure for performing functions or operations according to an embodiment or for implementing abstract data types according to an embodiment.

The program modules may be implemented using instructions or code executed by at least one processor of the encoding apparatus 1600.

The processing unit 1610 may execute instructions or code in the inter-prediction unit 110, the intra-prediction unit 120, the switch 115, the subtractor 125, the transform unit 130, the quantization unit 140, the entropy encoding unit 150, the dequantization unit 160, the inverse transform unit 170, the adder 175, the filter unit 180, and the reference picture buffer 190.

A storage unit may denote the memory 1630 and/or the storage 1640. Each of the memory 1630 and the storage 1640 may be any of various types of volatile or nonvolatile storage media. For example, the memory 1630 may include at least one of Read-Only Memory (ROM) 1631 and Random Access Memory (RAM) 1632.

The storage unit may store data or information used for the operation of the encoding apparatus 1600. In an embodiment, the data or information of the encoding apparatus 1600 may be stored in the storage unit.

For example, the storage unit may store pictures, blocks, lists, motion information, inter-prediction information, bitstreams, etc.

The encoding apparatus 1600 may be implemented in a computer system including a computer-readable storage medium.

The storage medium may store at least one module required for the operation of the encoding apparatus 1600. The memory 1630 may store at least one module, and may be configured such that the at least one module is executed by the processing unit 1610.

Functions related to communication of the data or information of the encoding apparatus 1600 may be performed through the communication unit 1220.

For example, the communication unit 1620 may transmit a bitstream to a decoding apparatus 1600, which will be described later.

FIG. 17 is a configuration diagram of a decoding apparatus according to an embodiment.

The decoding apparatus 1700 may correspond to the above-described decoding apparatus 200.

The decoding apparatus 1700 may include a processing unit 1710, memory 1730, a user interface (UI) input device 1750, a UI output device 1760, and storage 1740, which communicate with each other through a bus 1790. The decoding apparatus 1700 may further include a communication unit 1720 coupled to a network 1399.

The processing unit 1710 may be a Central Processing Unit (CPU) or a semiconductor device for executing processing instructions stored in the memory 1730 or the storage 1740. The processing unit 1710 may be at least one hardware processor.

The processing unit 1710 may generate and process signals, data or information that are input to the decoding apparatus 1700, are output from the decoding apparatus 1700, or are used in the decoding apparatus 1700, and may perform examination, comparison, determination, etc. related to the signals, data or information. In other words, in embodiments, the generation and processing of data or information and examination, comparison and determination related to data or information may be performed by the processing unit 1710.

The processing unit 1710 may include an entropy decoding unit 210, a dequantization unit 220, an inverse transform unit 230, an intra-prediction unit 240, an inter-prediction unit 250, a switch 245, an adder 255, a filter unit 260, and a reference picture buffer 270.

At least some of the entropy decoding unit 210, the dequantization unit 220, the inverse transform unit 230, the intra-prediction unit 240, the inter-prediction unit 250, the adder 255, the switch 245, the filter unit 260, and the reference picture buffer 270 of the decoding apparatus 200 may be program modules, and may communicate with an external device or system. The program modules may be included in the decoding apparatus 1700 in the form of an operating system, an application program module, or other program modules.

The program modules may be physically stored in various types of well-known storage devices. Further, at least some of the program modules may also be stored in a remote storage device that is capable of communicating with the decoding apparatus 1700.

The program modules may include, but are not limited to, a routine, a subroutine, a program, an object, a component, and a data structure for performing functions or operations according to an embodiment or for implementing abstract data types according to an embodiment.

The program modules may be implemented using instructions or code executed by at least one processor of the decoding apparatus 1700.

The processing unit 1710 may execute instructions or code in the entropy decoding unit 210, the dequantization unit 220, the inverse transform unit 230, the intra-prediction unit 240, the inter-prediction unit 250, the switch 245, the adder 255, the filter unit 260, and the reference picture buffer 270.

A storage unit may denote the memory 1730 and/or the storage 1740. Each of the memory 1730 and the storage 1740 may be any of various types of volatile or nonvolatile storage media. For example, the memory 1730 may include at least one of ROM 1731 and RAM 1732.

The storage unit may store data or information used for the operation of the decoding apparatus 1700. In an embodiment, the data or information of the decoding apparatus 1700 may be stored in the storage unit.

For example, the storage unit may store pictures, blocks, lists, motion information, inter-prediction information, bitstreams, etc.

The decoding apparatus 1700 may be implemented in a computer system including a computer-readable storage medium.

The storage medium may store at least one module required for the operation of the decoding apparatus 1700. The memory 1730 may store at least one module, and may be configured such that the at least one module is executed by the processing unit 1710.

Functions related to communication of the data or information of the decoding apparatus 1700 may be performed through the communication unit 1720.

For example, the communication unit 1720 may receive a bitstream from the encoding apparatus 1700.

FIG. 18 illustrates a col block in a col picture according to an example.

In FIG. 18 and subsequent drawings, “ColP” may represent a col picture. “ColB” may represent a col block.

Inter-prediction may be performed on a unit such as a PU, and the motion vector of the PU may be calculated through a process for predicting the motion of the PU. In order to reduce the number of bits required in order to represent a motion vector, a merge mode, an AMVP mode or the like may be used.

A merge mode may be a method that uses motion information of a neighbor block or a col block as motion information of a target block without change by copying the motion information of the neighbor block or the col block as the motion information of the target block. The motion information may include a motion vector.

The col block may be a block present at the same location as the target block within one of reference pictures that have been encoded or decoded before the target picture is encoded or decoded. Here, a reference picture including the col block may be referred to as a “col picture”. Here, the location may be a pixel location. Alternatively, the location of a block may be defined by the coordinates of the top-left location of the block.

In other words, the location of the col block in the col picture may be identical to the location of the target block in the target picture.

An AMVP mode may be a method that uses a motion vector, acquired from the neighbor block or col block of the target block, as a prediction motion vector for the motion vector of the target block, and encodes and/or decodes a motion vector difference. The motion vector difference may be the difference between the motion vector of the target block, calculated via motion prediction, and the prediction motion vector.

A Temporal Motion Vector Predictor (TMVP) may be a motion vector or motion information acquired from a col block or a block neighboring the col block.

When the AMVP mode is used, the TMVP may be a motion vector acquired from a col block or a block neighboring the col block or the motion vector of a temporal candidate. In other words, when the inter-prediction mode of the target block is the AMVP mode, the TMVP may be the motion vector of a temporal candidate.

When a merge mode is used, a TMVP may be motion information acquired from a col block or a block neighboring the col block, or may be motion information of a temporal candidate. In other words, when the inter-prediction mode of the target block is the merge mode, the TMVP may be motion information of a temporal candidate.

In FIG. 18, the area 1820 of a target block, a first location 1821, and a second location 1822 are depicted. The coordinates of a top-left location of the area 1820 of the target block may be (xP, yP), and the size of the area 1820 of the target block may be (nPSW, nPSH).

A TMVP may be acquired from a first col block disposed at the first location 1821. The first col block may be a block that occupies the first location 1821. For example, the first location 1821 may be a bottom-right location of the target block. Alternatively, the first location may be defined by coordinates (xP+nPSW, yP+nPSH).

The TMVP may be acquired from a second col block disposed at the second location 1822. The second col block may be a block that occupies the second location 1822. For example, the second location 1822 may be the location of the center of the target block. Alternatively, the second location may be defined by the coordinates (xP+(nPSW>>1), yP+(nPSH>>1)).

The higher the accuracy of a TMVP, the greater the gain that can be obtained using the TMVP. Here, the accuracy of a TMVP being high may mean that the TMVP is closer to the motion vector of the target block.

When an object is moving faster in an image, the magnitude of the motion vector of a block indicating the object may be increased. When such a block is used as a temporal candidate, the magnitude of a derived TMVP may be large. Further, when the magnitude of the TMVP is large, the accuracy of the TMVP may be greatly deteriorated.

In the following embodiments, a Unilateral Temporal Motion Vector Predictor (UTMVP) that replaces a TMVP to enhance encoding efficiency will be described.

A UTMVP may be acquired from motion vectors in a col picture. By utilizing the UTMVP, an error rate or the like may be reduced in relation to the determination of the motion vector of a target block.

FIG. 19 illustrates a TMVP acquisition process according to an example.

In FIG. 19, a process for acquiring a TMVP having small motion is illustrated.

A col block 1921 for a target block 1911 may be present at the same location as the target block 1911 present in a target picture 1910. In other words, the target block 1911 and the col block 1921 may be co-located. The col block 1921 may be a block present in a col picture 1920.

The motion vector 1922 of the col block 1921 may be scaled in the direction of the target picture 1910 and a reference picture 1930, and the scaled motion vector may be used as the TMVP 1912 of the target block 1911.

For example, when the magnitude of the TMVP 1912 is small, the scaled motion vector may not greatly deviate from the target block 1911 when the motion vector 1922 of the col block 1921 is scaled from the col picture 1920 to the target picture 1910.

Hereinafter, in embodiments that refer to FIG. 19 and subsequent drawings, the target block may be a specific type of target unit. For example, the target block may be a target PU.

FIG. 20 illustrates a TMVP acquisition process and a UTMVP acquisition process according to an example.

In FIG. 20, a process for acquiring a TMVP having large motion is illustrated.

When the motion vector 2022 of a col block 2021 for a target block 2011 is scaled in the direction from a col picture 2020 to a target picture 2010, the scaled motion vector may greatly deviate from the target block 2011. In this case, the difference between a TMVP 2019 and the actual motion vector of the target block 2011 may be large.

In order to solve the above problem, the difference between a UTMVP 2012 and the actual motion vector of the target block 2011 may be decreased by exploiting the UTMVP 2012 instead of the TMVP 2019. The UTMVP 2012 may be generated based on the motion vector 2024 of a block 2023 present in the col picture 2020.

In an embodiment, a UTMVP generation method may mean the following steps 1) to 4).

Step 1) For candidate blocks in a col picture, the motion vector of at least one candidate block may be scaled to the target picture, and thus a first scaled motion vector may be generated. Hereinafter, in embodiments that refer to FIG. 20 and subsequent drawings, each candidate block may be a specific type of unit in a col picture. For example, the candidate block may be a candidate PU.

In the candidate block, the term “candidate” may mean that the motion vector of the corresponding block has the possibility of being used to generate the UTMVP of a target block, but whether the motion vector is to be actually used is not yet determined.

Step 2) Whether the first scaled motion vector indicates the target block may be determined.

Step 3) When the first scaled motion vector indicates the target block, a second scaled motion vector may be generated by scaling the motion vector of the candidate block in the direction from the target picture to a reference picture.

Step 4) The second scaled motion vector may be used as a UTMVP.

FIG. 21 illustrates a UTMVP generation process according to an example

In FIG. 21, the location 2113 at which the motion vector 2124 of a candidate block 2123 in a col picture 2120 passes through a target picture 2110 is illustrated. Also, in FIG. 21, a reference picture 2130 for a target block 2111 is illustrated.

As illustrated in the drawing, the location 2113 is present in a target block 2111. In other words, the motion vector 2124 passes through the target block 2111.

Since the motion vector 2124 passes through the target block 2111 of the target picture 2110, the motion vector 2124 may be used to generate a UTMVP, and a UTMVP 2112 may be generated by applying scaling to the motion vector 2124.

FIG. 22 illustrates a UTMVP generation process according to an example.

In FIG. 22, the motion vector 2224 of a candidate block 2223 in a col picture 2220 is depicted. Further, in FIG. 22, a reference picture 2240 for the candidate block 2223 and a reference picture 2230 for a target block 2211 are depicted.

The motion vector 2224 of the candidate block 2223 may be scaled in the direction from the col picture 2220 to a target picture 2210. The location 2213 at which the scaled motion vector passes through the target picture 2210 is illustrated. As illustrated in the drawing, the scaled motion vector passes through the target block 2211.

Since the scaled motion vector passes through the target block 2211, the motion vector 2224 may be used to generate a UTMVP 2212, and the UTMVP 2212 may be generated by applying scaling to the motion vector 2224.

FIG. 23 is a flowchart of an inter-prediction method performed by a decoding apparatus according to an embodiment.

The inter-prediction method according to the present embodiment may be understood to be a decoding method.

At step 2310, the communication unit 1720 of a decoding apparatus 1700 may receive a bitstream including inter-prediction information.

At step 2320, the processing unit 1710 of the decoding apparatus 1700 may generate a motion vector predictor of a target block.

The motion vector predictor may be the above-described UTMVP. Alternatively, the motion vector predictor may be a UTMVP used as the above-described TMVP. When the UTMVP satisfies a specified condition, the UTMVP may be used as a TMVP.

The processing unit 1710 may generate a motion vector predictor of the target block based on the motion vector of a candidate block in a col picture for the target block.

For example, the processing unit 1710 may generate the motion vector predictor of the target block using one or more of 1) motion information of a candidate block in a col picture, 2) the motion vector of the candidate block, 3) the location of the candidate block in the col picture, 4) the location of the target block in the target picture, 5) the location of the candidate block relative to the target block, 6) the Picture Order Count (POC) of the col picture, 7) the POC of a reference picture for the candidate block, 8) the POC of the target picture, 9) the POC of a reference picture for the target block, 10) a first temporal distance from the col picture to the target picture, 11) a second temporal distance from the col picture to the reference picture for the candidate block, 12) the ratio of the first temporal distance to the second temporal distance, 13) a third temporal distance from the target picture to the reference picture for the target block, 14) the ratio of the third temporal distance to the second temporal distance, 15) a first difference, which is the difference between the POC of the target picture and the POC of the col picture, 16) a second difference, which is the difference between the POC of the reference picture for the candidate block and the POC of the col picture, 17) the ratio of the first difference to the second difference, and 18) a third difference, which is the difference between the POC of the reference picture for the target block and the POC of the target picture. Here, the POC of a specified picture may mean the location of the corresponding picture among the pictures.

In an embodiment, the processing unit 1710 may determine whether a motion vector predictor is to be generated based on the inter-prediction mode of inter-prediction information for the target block.

For example, the processing unit 1710 may generate a motion vector predictor when the inter-prediction mode is an AMVP mode, a merge mode, or a skip mode. In other words, the processing unit 1710 may generate motion vector predictors for one or more specified inter-prediction modes, among the AMVP mode, the merge mode, and the skip mode.

As described above, the skip mode and the merge mode may be identical or similar to each other except as to whether a reconstructed residual block is used. Hereinafter, a description of the merge mode may also be applied to the skip mode.

In an embodiment, the generated motion vector predictor may be added as a candidate to a list for a target block. The list may include one or more candidates. The inter-prediction information may include an index for the list. The index for the list may indicate which candidate of one or more candidates in the list is to be used for inter-prediction.

For example, when the inter-prediction mode of inter-prediction information indicates an AMVP mode, the AMVP mode may be used for the target block. The motion vector predictor may be a prediction motion vector candidate in the AMVP mode. The motion vector predictor may be added, as a prediction motion vector candidate, to a motion vector candidate list.

For example, when the inter-prediction mode of inter-prediction information indicates a merge mode, the merge mode may be used for the target block. The motion vector predictor may be motion information in the merge mode. Alternatively, the motion information in the merge mode may include a motion vector predictor. The motion vector predictor may be added as motion information or as part of the motion information to a merge candidate list.

At step 2330, the processing unit 1710 may perform inter-prediction for the target block based on the motion vector predictor.

For example, when an AMVP mode is used for the target block and a prediction motion vector index of the inter-prediction information indicates a motion vector predictor, the processing unit 1710 may perform inter-prediction for the target block using a motion vector predictor present in the motion vector candidate list.

For example, when a merge mode is used for the target block and the merge index of inter-prediction information indicates a motion vector predictor, the processing unit 1710 may perform inter-prediction for the target block using a motion vector predictor present in the merge candidate list.

The processing unit 1710 may generate a prediction block for the target block by performing inter-prediction for the target block based on the motion vector predictor.

The processing unit 1710 may generate a reconstructed block by adding the prediction block to the reconstructed block.

FIG. 24 is a flowchart of an inter-prediction method performed by an encoding apparatus according to an embodiment.

The inter-prediction method according to the present embodiment may be understood to be an encoding method.

According to the principle of image encoding, an encoding apparatus 1600 must be able to generate a reconstructed block for a target block in the same manner as the decoding apparatus 1700. Further, since a reconstructed block generated by the decoding apparatus 1700 and a reconstructed block generated by the encoding apparatus 1600 must be identical to each other, at least a part of the inter-prediction method, described above with reference to FIG. 16, may be equally performed by the encoding apparatus 1600.

At step 2410, the processing unit 1610 of the decoding apparatus 1600 may generate a motion vector predictor of a target block.

The motion vector predictor may be the above-described UTMVP. Alternatively, the motion vector predictor may be a UTMVP used as the above-described TMVP. When the UTMVP satisfies a specified condition, the UTMVP may be used as the TMVP.

The processing unit 1610 may generate the motion vector predictor of the target block based on the motion vector of a candidate block in a col picture.

For example, the processing unit 1610 may generate the motion vector predictor of the target block based on one or more of 1) motion information of a candidate block in a col picture, 2) the motion vector of the candidate block, 3) the location of the candidate block in the col picture, 4) the location of the target block in the target picture, 5) the location of the candidate block relative to the target block, 6) the Picture Order Count (POC) of the col picture, 7) the POC of a reference picture for the candidate block, 8) the POC of the target picture, 9) the POC of a reference picture for the target block, 10) a first temporal distance from the col picture to the target picture, 11) a second temporal distance from the col picture to the reference picture for the candidate block, 12) the ratio of the first temporal distance to the second temporal distance, 13) a third temporal distance from the target picture to the reference picture for the target block, 14) the ratio of the third temporal distance to the second temporal distance, 15) a first difference, which is the difference between the POC of the target picture and the POC of the col picture, 16) a second difference, which is the difference between the POC of the reference picture for the candidate block and the POC of the col picture, 17) the ratio of the first difference to the second difference, and 18) a third difference, which is the difference between the POC of the reference picture for the target block and the POC of the target picture. Here, the POC of a specified picture may mean the location of the corresponding picture among the pictures.

As described above, the skip mode and the merge mode may be identical or similar to each other except as to whether a reconstructed residual block is used. Hereinafter, the description of the merge mode may also be applied to the skip mode.

In an embodiment, the generated motion vector predictor may be added as a candidate to a list. The list may include one or more candidates.

For example, the processing unit 1600 may use an AMVP mode for the target block. Here, the inter-prediction mode of inter-prediction information may indicate an AMVP mode. When the AMVP mode is used, the motion vector predictor may be a prediction motion vector candidate in the AMVP mode. The motion vector predictor may be added, as a prediction motion vector candidate, to a motion vector candidate list.

For example, the processing unit 1600 may use a merge mode for the target block. Here, the inter-prediction mode of inter-prediction information may indicate the merge mode. When the merge mode is used, the motion vector predictor may be motion information of the merge mode. Alternatively, the motion information of the merge mode may include a motion vector predictor. The motion vector predictor may be added, as motion information or as part of the motion information, to a merge candidate list.

At step 2420, the processing unit 1610 may generate inter-prediction information based on the motion vector predictor.

The inter-prediction mode of the inter-prediction information may indicate whether a motion vector predictor is to be generated.

For example, when the inter-prediction mode indicates that an AMVP mode, a merge mode or a skip mode is used for inter-prediction of the target block, the inter-prediction mode may indicate that the motion vector predictor of the target block is to be generated.

For example, when an AMVP mode, a merge mode or a skip mode is used for inter-prediction of the target block in the encoding apparatus 1600, the inter-prediction mode may indicate that an AMVP mode, a merge mode or a skip mode is used for inter-prediction of the target block, and with the use of the AMVP mode, the merge mode or the skip mode, the motion vector predictor may also be used in the decoding apparatus 1700.

The inter-prediction information may include an index for a list. The index for the list may indicate which candidate of one or more candidates in the list is to be used for inter-prediction. Alternatively, among one or more candidates in the list, a candidate indicated by the index for the list may be identical to the motion vector predictor used for inter-prediction.

At step 2430, the communication unit 1620 of the encoding apparatus 1600 may transmit a bitstream including the inter-prediction information to the decoding apparatus 1700.

At step 2440, the processing unit 1610 may perform inter-prediction for the target block based on the motion vector predictor.

For example, when the AMVP mode is used for the target block, the processing unit 1610 may perform inter prediction for the target block using the motion vector predictor. Here, the prediction motion vector index may indicate a motion vector predictor, among prediction motion vector candidates in the motion vector candidate list. Alternatively, among the prediction motion vector candidates, a prediction motion vector candidate indicated by the prediction motion vector index may be identical to the motion vector predictor.

For example, when the merge mode is used for the target block, the processing unit 1610 may perform inter-prediction for the target block using the motion vector predictor. Here, a merge index may indicate motion information including the motion vector predictor, among pieces of motion information in a merge list. Alternatively, the motion vector of motion information indicated by the merge index, among the pieces of motion information in the merge list, may be identical to the motion vector predictor.

Alternatively, the processing unit 1610 may perform inter-prediction for the target block using the motion vector of the target block. Here, the motion vector of the target block and the motion vector predictor may have a specified relationship therebetween.

For example, when the inter-prediction mode indicates that an AMVP mode is used for inter-prediction of the target block, the motion vector of the target block may be equal to the sum of the motion vector predictor and the motion vector difference of inter-prediction information. Alternatively, the motion vector of the target block may be generated based on the motion vector predictor and the motion vector difference of inter-prediction information.

For example, when the inter-prediction mode indicates that a merge mode is used for inter-prediction of the target block, the motion vector of the target block may be identical to the motion vector predictor.

The processing unit 1610 may generate a prediction block for the target block by performing inter-prediction for the target block.

The processing unit 1610 may generate a reconstructed block by adding the prediction block to the reconstructed block.

Methods for Generating UTMVP

Various methods may be used to acquire a UTMVP. The UTMVP generated through various methods including the methods to be described below may be used as a TMVP of a target block. Hereinafter, the term “UTMVP candidate” may be used to have the same meaning as the term “UTMVP”.

The following Code 1 may indicate a first method for generating a UTMVP.

[Code 1] Algorithm 1 UTMVP derivation process of the current PU  1: procedure DERIVEUTMVP  2:  for PU p in ColP do  3:   scaleDst = (curPOC − colPOC)/(p.refPOC − colPOC)  4:   dstPt = p.mv * scaleDst  5:   if isInboundOfCurrentPU(dstPt) then  6:    scaleSrc = (refPOC − curPOC)/(p.refPOC − colPOC)  7:    Return p.mv * scaleSrc  8:   end if  9:  end for 10:  Return NotAvail 11: end procedure

In Code 1, procedure DeriveUTMVP may return a generated UTMVP or a value indicating that a UTMVP is unavailable.

In Code 1, “current PU” may indicate a PU that is a target block.

In Code 1, “p” may indicate a PU that is a candidate block in a col picture. The candidate block may be any one of blocks in the col picture. “ColP” may indicate a col picture.

In Code 1, “curPOC” may indicate the POC of a target picture including the target block. “ColPOC” may indicate the POC of the col picture. “p.refPOC” may indicate the POC of a reference picture for a candidate block. “refPOC” may indicate the POC of a reference picture for the target block. The reference picture for the candidate block may indicate a picture referred to by the candidate block. The reference picture for the target block may indicate a picture referred to by the target block.

In Code 1, “scaleDST” may indicate a first scaling coefficient.

In Code 1, “p.mv” may indicate the motion vector of the candidate block. “dstPt” may indicate a first scaled motion vector.

In Code 1, the function “isInboundOfCurrentPU(dstPt)” may return information related to whether an input motion vector dstPt indicates the target block of a target picture. Alternatively, the function “isInboundOfCurrentPU(dstPt)” may return information related to whether the location indicated by the input motion vector dstPt is included in the target block.

In Code 1, “scaleSrc” may indicate a second scaling coefficient. The product of “p.mv” and “scaleSrc” may indicate a second scaled motion vector. The second scaled motion vector may be the UTMVP of the target block.

FIG. 25 is a flowchart of a method for generating a motion vector predictor of a target block according to an embodiment.

Step 2330, described above with reference to FIG. 23, may include the following steps 2510 and 2520. Also, step 2410, described above with reference to FIG. 24, may include the following steps 2510 and 2520.

At step 2510, a processing unit may determine whether motion information of a candidate block is to be used to generate a motion vector predictor of a target block.

If it is determined that the motion information of the candidate block is to be used to generate the motion vector predictor of the target block, step 2520 may be performed.

If it is determined that the motion information of the candidate block is not to be used to generate the motion vector predictor of the target block, a process for the current candidate block may be terminated.

The processing unit may determine, based on a specified condition, whether the motion information of the candidate block is to be used to generate the motion vector predictor of the target block.

For example, the processing unit 1610 may determine whether to generate the motion vector predictor of the target block based on one or more of 1) motion information of a candidate block in a col picture, 2) the motion vector of the candidate block, 3) the location of the candidate block in the col picture, 4) the location of the target block in the target picture, 5) the location of the candidate block relative to the target block, 6) the Picture Order Count (POC) of the col picture, 7) the POC of a reference picture for the candidate block, 8) the POC of the target picture, 9) the POC of a reference picture for the target block, 10) a first temporal distance from the col picture to the target picture, 11) a second temporal distance from the col picture to the reference picture for the candidate block, 12) the ratio of the first temporal distance to the second temporal distance, 13) a first difference, which is the difference between the POC of the target picture and the POC of the col picture, 14) a second difference, which is the difference between the POC of the reference picture of the candidate block and the POC of the col picture, and 15) the ratio of the first difference to the second difference. Here, the POC of a specified picture may mean the location of the corresponding picture among the pictures.

At step 2520, the processing unit may generate the motion vector predictor of the target block based on the motion information of the candidate block.

In other words, the motion information of the candidate block may be used to generate the motion vector predictor of the target block.

FIG. 26 is a flowchart of a method for determining whether motion information of a candidate block is to be used to generate a motion vector predictor.

Step 2510, described above with reference to FIG. 25, may include steps 2610, 2620, and 2630.

At step 2610, a processing unit may calculate a first scaling coefficient for the motion vector of a candidate block.

The first scaling coefficient may be a value obtained by dividing a first temporal distance by a second temporal distance. Further, the first scaling coefficient may be the ratio of the first temporal distance to the second temporal distance. The first temporal distance may be a temporal distance from a col picture to a target picture. The second temporal distance may be a temporal distance from the col picture to a reference picture for the candidate block.

Alternatively, the distance between pictures may be represented by the difference between the POCs of the pictures. The first scaling coefficient may be a value obtained by dividing a first difference by a second difference. Alternatively, the first scaling coefficient may be the ratio of the first difference to the second difference. The first difference may be the difference between the POC of the target picture and the POC of the col picture. The second difference may be the difference between the POC of the reference picture for the candidate block and the POC of the col picture.

At step 2620, the processing unit may generate a first scaled motion vector by applying first scaling to the motion vector of the candidate block.

The processing unit may generate the first scaled motion vector by multiplying the first scaling coefficient by the motion vector of the candidate block. In other words, the first scaled motion vector may be the product of the motion vector of the candidate block and the first scaling coefficient.

The first scaling coefficient may be a coefficient for scaling the motion vector of the candidate block depending on the temporal direction between the target picture and a reference picture for the target block.

The first scaled motion vector may indicate a location in the target picture indicated by the motion vector of the candidate block.

At step 2630, the processing unit may determine whether the first scaled motion vector indicates the target block.

For example, when the departure (source) location of the first scaled motion vector is the candidate block, if the arrival location of the first scaled motion vector is included in the area of the target block, the first scaled motion vector may indicate the target block.

For example, when the departure location of the first scaled motion vector is the candidate block, if the arrival location of the first scaled motion vector is not included in the area of the target block, the first scaled motion vector may not indicate the target block.

For example, when the sum of the location of the candidate block and the first scaled motion vector is included in the area of the target block, the first scaled motion vector may indicate the target block. For example, when the sum of the location of the candidate block and the first scaled motion vector deviates from the area of the target block, the first scaled motion vector may not indicate the target block.

If it is determined that the first scaled motion vector indicates the target block, the motion information of the candidate block may be used to generate the motion vector predictor of the target block, and step 2520 may be performed.

If it is determined that the first scaled motion vector does not indicate the target block, the motion information of the candidate block may not be used to generate the motion vector predictor of the target block, and a process for the current candidate block may be terminated.

FIG. 27 is a flowchart of a method for generating a motion vector predictor of a target block based on motion information of a candidate block according to an embodiment.

Step 2520, described above with reference to FIG. 25, may include steps 2710 and 2720.

At step 2710, a processing unit may calculate a second scaling coefficient for the motion vector of a candidate block.

The second scaling coefficient may be a value obtained by dividing a third temporal distance by a second temporal distance. Alternatively, the second scaling coefficient may be the ratio of the third temporal distance to the second temporal distance. The third temporal distance may be a temporal distance from a target picture to a reference picture for a target block. The second temporal distance may be a temporal distance from a col picture to a reference picture for the candidate block.

Alternatively, the distance between pictures may be represented by the difference between the POCs of the pictures. The second scaling coefficient may be a value obtained by dividing a third difference by a second difference. Alternatively, the third scaling coefficient may be the ratio of the third difference to the second difference. The third difference may be the difference between the POC of a reference picture for the target block and the POC of a target picture. The second difference may be the difference between the POC of the reference picture for the candidate block and the POC of the col picture.

At step 2720, the processing unit may generate a motion vector predictor by applying second scaling to the motion vector of the candidate block.

The processing unit may generate the motion vector predictor by multiplying the second scaling coefficient by the motion vector of the candidate block. In other words, the motion vector predictor may be the product of the motion vector of the candidate block and the second scaling coefficient.

Use of multiple motion vector predictors by multiple candidate blocks

As described above, a motion vector predictor may be calculated for a specified candidate block.

A candidate block may include multiple candidate blocks. Steps 2510 and 2520 of FIG. 25 may be performed on the multiple candidate blocks in a specific sequence.

Steps 2510 and 2520 of FIG. 25 may be performed on each of the multiple candidate blocks. For each candidate block, whether a motion vector predictor is to be generated using the motion vector of the corresponding candidate block may be determined at step 2510.

The motion vector used to generate a motion vector predictor may be referred to as an “available motion vector”. The available motion vector may be a motion vector that satisfies a specified condition. The specified condition may be a condition indicating whether a first scaled vector, generated by applying first scaling to the motion vector of the candidate block, indicates a target block. Alternatively, the specified condition may be a condition indicating whether the trajectory of the motion vector of the candidate block penetrates into the target block. In other words, the first scaled vector generated using the available motion vector may indicate the target block. Alternatively, the trajectory of the available motion vector may penetrate through the target block.

The motion vector that is not used to generate a motion vector predictor may be referred to as an “unavailable motion vector”. The unavailable motion vector may be a motion vector that does not satisfy a specified condition.

At steps 2510 and 2520, the motion vector predictor may be generated based on multiple available motion vectors of multiple candidate blocks.

In an embodiment, a motion vector, which is a first target of calculation, among the multiple available motion vectors, may be used to generate a motion vector predictor.

In an embodiment, the average value of the multiple available motion vectors may be used to generate a motion vector predictor. In other words, the motion vector predictor may be the product of the average value and the second scaling coefficient.

In an embodiment, the average value of one or more of the multiple available motion vectors may be used to generate a motion vector predictor. In other words, the motion vector predictor may be the product of the average value and the second scaling coefficient.

In an embodiment, an available motion vector, which is used to generate a first scaled vector that reaches a location closest to the specific location, among the multiple available motion vectors, may be used to generate a motion vector predictor. The specific location may be the center of the target block. Alternatively, the specific location may be a specific location within the target block.

In an embodiment, a motion vector having the lowest Sum of Absolute Differences (SAD), among the multiple available motion vectors, may be used to generate a motion vector predictor. Here, SAD may be the SAD between a reconstructed block for a candidate block having an available motion vector and a reconstructed block indicated by the available motion vector.

In an embodiment, one or more available motion vectors may be selected from among multiple available motion vectors based on the inter-prediction indicator of the target block, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

For example, when the inter-prediction indicator of the target block indicates L0 prediction, one or more available motion vectors of one or more candidate blocks that refer to reference pictures in reference picture list L0 of the target block, among the multiple available motion vectors, may be used to generate a motion vector predictor.

For example, when the inter-prediction indicator of the target block indicates L1 prediction, one or more available motion vectors of one or more candidate blocks that refer to reference pictures in reference picture list L1 of the target block, among the multiple available motion vectors, may be used to generate a motion vector predictor.

In an embodiment, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks based on the inter-prediction indicators of multiple candidate blocks in a col picture, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

For example, when the inter-prediction indicator of a candidate block in a col picture indicates specific prediction, a motion vector corresponding to the specific prediction of the candidate block may be used to generate a motion vector predictor. For example, the specific prediction may be L0 prediction, and the corresponding motion vector may be an L0 motion vector of the candidate block. Alternatively, the specific prediction may be L1 prediction, and the corresponding motion vector may be an L1 motion vector of the candidate block.

In an embodiment, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks based on the reference picture index of the target block, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

For example, when the reference picture index of the target block indicates a specific reference picture, one or more available motion vectors of one or more candidate blocks that refer to the specific reference picture, among multiple candidate blocks, may be used to generate a motion vector predictor. For example, the specific reference picture may be a first reference picture in reference picture list L0. Alternatively, the specific reference picture may be a first reference picture in reference picture list L1.

In an embodiment, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks based on reference picture indices of candidate blocks in a col picture, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

For example, when the reference picture index of the candidate block indicates a specific reference picture, a motion vector corresponding to the reference picture index of the candidate block may be used to generate a motion vector predictor. For example, the specific reference picture may be a first reference picture in reference picture list L0, and the corresponding motion vector may be an L0 motion vector. Alternatively, the specific reference picture may be a first reference picture in reference picture list L1, and the corresponding motion vector may be an L1 motion vector.

In an embodiment, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks based on the POC of the target picture, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

For example, based on a comparison between the POC of the target picture and the POC of a candidate block, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined. Here, the POC of the candidate block may be the POC of a reference picture referred to by the candidate block.

For example, when the POC of the target picture is less than the POC of the candidate block, the available motion vector of the candidate block may be used to generate a motion vector predictor.

In an embodiment, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks based on the POC of a col picture, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

For example, based on a comparison between the POC of the col picture and the POC of the candidate block, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined. Here, the POC of the candidate block may be the POC of a reference picture referred to by the candidate block.

For example, when the POC of the col picture is greater than the POC of the candidate block, the available motion vector of the candidate block may be used to generate a motion vector predictor.

In an embodiment, based on the magnitude of a motion vector related to the candidate block, whether the available motion vector of the candidate block is to be used to generate the motion vector predictor may be determined. Here, the related motion vector may be the motion vector of the candidate block, the first scaled motion vector of the candidate block, or the motion vector predictor of the candidate block.

For example, based on a comparison between the magnitude of the motion vector related to the candidate block and a predefined threshold, whether the available motion vector of the candidate block is to be used to generate the motion vector predictor may be determined.

For example, when the magnitude of the motion vector related to the candidate block is less than the predefined threshold, the available motion vector of the candidate block may be used to generate the motion vector predictor.

In an embodiment, for a specific inter-prediction direction, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined. The specific inter-prediction direction may be the L0 direction or the L1 direction.

For example, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks for the L0 direction, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

For example, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks for the L1 direction, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

In an embodiment, depending on the slice type of the target block or the slice type of the candidate block, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined. The slice type may be a P slice or a B slice.

In an embodiment, based on the size of the target block, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined.

For example, based on a comparison between the size of the target block and a predefined size, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined.

For example, when the size of the target block is less than a predefined size M×N, the available motion vector of the candidate block may be used to generate a motion vector predictor. For example, when the size of the target block is greater than the predefined size M×N, the available motion vector of the candidate block may be used to generate a motion vector predictor. Each of M and N may be a positive integer.

In an embodiment, depending on the inter-prediction mode of the target block, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined.

For example, when the inter-prediction mode of the target block is a specific mode, the available motion vector of the candidate block may be used to generate a motion vector predictor.

For example, when the inter-prediction mode of the target block is a merge mode, the available motion vector of the candidate block may be used to generate a motion vector predictor.

For example, when the inter-prediction mode of the target block is a skip mode, the available motion vector of the candidate block may be used to generate a motion vector predictor.

For example, when the inter-prediction mode of the target block is an AMVP mode, the available motion vector of the candidate block may be used to generate a motion vector predictor.

In an embodiment, based on at least one of coding parameters of the target block, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined.

In an embodiment, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks based on at least one of the coding parameters of the target block, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

In an embodiment, based on at least one of coding parameters of the candidate block, whether the available motion vector of the candidate block is to be used to generate a motion vector predictor may be determined.

For example, one or more available motion vectors may be selected from among available motion vectors of multiple candidate blocks based on at least one of the coding parameters of the candidate block, and the selected one or more available motion vectors may be used to generate a motion vector predictor.

One or more of the methods for determining use or non-use according to the above-described embodiments may be combined with each other.

In accordance with the embodiments, described above with reference to FIGS. 25 to 27, motion vector predictors may be calculated for all candidate blocks in a col picture with respect to a single target block. That is, when a target block is changed, the above process is repeated for the changed target block, and thus the motion vector predictors may be calculated for all candidate blocks. Such repetition may greatly increase the computational complexity of encoding and/or decoding.

The following Code 2 may indicate a second method for generating a UTMVP.

[Code 2] Algorithm 2 UTMVP derivation process procedure DERIVEUTMVPSET  2:  UTMVPSet[numberOfPUsInPicture]  for PU p in ColP do  4:   scaleDst = (curPOC − colPOC)/(p.refPOC − colPOC)   dstPt = p.mv * scaleDst  6:   cP = PU of currentPicture at dstPt   scaleSrc = (refPOC − curPOC)/(p.refPOC − colPOC)  8:   UTMVPSet[cP] = p.mv * scaleSrc  end for 10:  Return UTMVPSet end procedure

In Code 2, for each of all candidate blocks in a col picture, a first scaled motion vector may be generated using the motion vector of the corresponding candidate block, and a destination block indicated by the first scaled motion vector, among blocks in the target picture, may be identified. The motion vector of the candidate block may be used to generate a motion vector predictor of the identified destination block.

In the symbols appearing in common in Codes 1 and 2, the meaning of the symbols may be identical to those explained in connection with the above-described Code 1.

In Code 2, “numberOfPUsInPicture” may indicate the total number of blocks in the target picture. Alternatively, “numberOfPUsInPicture” may indicate the number of blocks resulting from partitioning when the target picture is partitioned into blocks, each having an N×N size. N may be a positive integer.

In Code 2, “UTMVPSet” may denote memory which stores the UTMVP of the corresponding block for each of blocks in the target picture. The memory may indicate an array. “UTMVPSet[cP]” may denote the UTMVP of block cP.

In Code 2, “cP” may denote a destination block indicated by “dstPt”, among blocks in the target picture.

FIG. 28 is a flowchart of a method for generating a motion vector predictor of a target block according to an embodiment.

Step 2330, described above with reference to FIG. 23, may include the following steps 2810, 2820, 2830, 2840, 2850, and 2860. Also, step 2410, described above with reference to FIG. 24, may include steps 2810, 2820, 2830, 2840, 2850, and 2860.

A processing unit may perform the following steps 2810, 2820, 2830, 2840, 2850, and 2860 on each of all candidate blocks in a col picture.

Alternatively, the processing unit may perform the following steps 2810, 2820, 2830, 2840, 2850, and 2860 on each of some candidate blocks selected from the col picture.

In an embodiment, a target block may be used to specify a target picture. In contrast, the motion vector predictor generated in the embodiment may be set to the motion vector predictor of a destination block other than the target block.

For example, some selected candidate blocks may include the candidate block, which has been described as being selected based on a specified condition in the above-described embodiments, and may include the candidate block having a motion vector, which has been described as being selected based on a specified condition in the above-described embodiments.

For example, the processing unit may initialize the memory. For blocks in the target picture, the memory may store the motion vector predictor of each of the blocks.

At step 2810, the processing unit may calculate a first scaling coefficient for the motion vector of the candidate block.

Step 2810 may correspond to step 2610, described above with reference to FIG. 26. Repetitive descriptions will be omitted here.

At step 2820, the processing unit may generate a first scaled motion vector by applying first scaling to the motion vector of the candidate block.

Step 2820 may correspond to step 2620, described above with reference to FIG. 26. Repetitive descriptions will be omitted here.

At step 2830, the processing unit may identify a destination block indicated by the first scaled motion vector, among the blocks of the target picture.

For example, when the departure location of the first scaled motion vector is the candidate block, the destination block may be a block including the arrival location of the first scaled motion vector, among the blocks present in the target picture.

For example, the destination block may be a block including the location indicated by the sum of the location of the candidate block and the first scaled motion vector, among the blocks present in the target picture.

At step 2840, the processing unit may calculate a second scaling coefficient for the motion vector of the candidate block.

Step 2840 may correspond to step 2710, described above with reference to FIG. 27. Repetitive descriptions will be omitted here.

At step 2850, the processing unit may generate a motion vector predictor by applying second scaling to the motion vector of the candidate block.

Step 2850 may correspond to step 2720, described above with reference to FIG. 27. Repetitive descriptions will be omitted here.

At step 2860, the processing unit may set the generated motion vector predictor as the motion vector predictor of the destination block. Through this setting, when the destination block is the target block, the motion vector predictor generated at step 2850 may be the motion vector predictor of the target block.

For example, the processing unit may add the motion vector predictor to an element indicating a destination block, among the elements of the memory. The element indicating the destination block may be an element determined to be the target to be accessed by an index for the memory, among the elements of the memory, when the index for the memory is the destination block or the identifier of the destination block.

For example, when the destination block identified at step 2830 is the target block, the generated motion vector predictor may be set as the motion vector predictor of the target block.

Through the repetition of the above-described steps 2810, 2820, 2830, 2840, 2850 and 2860, the motion vector predictor of the destination block may be generated using the motion vector of the corresponding candidate block for each of all candidate blocks in a col picture or some candidate blocks selected from the col picture. At this time, a first scaled motion vector may be derived using the motion vector of each candidate block, and the destination block indicated by the first scaled motion vector may be identified.

In the embodiment, steps 2810, 2820, 2830, 2840, 2850 and 2860 in the embodiment may be performed on each of multiple reference picture lists.

For example, when the slice type of the target picture is a B slice, steps 2810, 2820, 2830, 2840, 2850 and 2860 may be performed on each of reference picture list L0 and reference picture list L1. In this case, the memory may include multiple memories, which may be used for respective ones among the multiple reference picture lists.

The following Code 3 may indicate a third method for generating a UTMVP.

[Code 3] Algorithm 3 UTMVP derivation process of the current PU procedure DERIVEUTMVP(x, y)  if ||TMVP|| < T then  3:   Return NotAvail  end if  for Pu p in ColP where abs(p.x − x) < S and abs(p.y − y) < S) do  6:   scaleDst = (curPOC − colPoc)/(p.refPOC − colPOC)   dstPt = p.mv * scaleDst   if isInboundOfCurrentPU(dstPt) then  9:    scaleSrc = (refPOC − curPOC)/(p.refPOC − colPOC)    Return p.mv * scaleSrc   end if 12:  end for  Return NotAvail end procedure

In Code 3, a condition for initiating the calculation of a UTMVP of a target block and a condition for selecting a candidate block are added. Since UTMVPs are derived only for a target block and a candidate block that satisfy these conditions, a computational load of encoding and/or decoding using Code 3 may be decreased further than that of encoding and/or decoding using Code 1.

In the symbols appearing in common in Codes 1 and 3, the meaning of the symbols may be identical to those explained in connection with the above-described Code 1.

In Code 3, “x” and “y” may indicate coordinates of the target block.

In Code 3, “TMVP” may be the TMVP of the target block. “∥ ∥” may be a function for returning the magnitude of an input value. “T” may indicate a first threshold.

In Code 3, “p.x” and “p.y” may indicate the coordinates of the candidate block.

In Code 3, “abs( )” may be a function of returning the absolute value of the input value.

In Code 3, “S” may indicate a second threshold.

FIG. 29 is a flowchart of a method for generating a motion vector predictor of a target block using a specified condition according to an embodiment.

Step 2330, described above with reference to FIG. 23, may include the following steps 2910, 2920, 2930, and 2940. Also, step 2410, described above with reference to FIG. 24, may include the following steps 2910, 2920, 2930, and 2940.

At step 2910, a processing unit may determine whether to derive a motion vector predictor of the target block.

The processing unit may determine whether a motion vector predictor of the target block is to be derived depending on a specified condition.

In an embodiment, the processing unit may determine, based on the result of a comparison between the magnitude of the TMVP of the target block and a first threshold, whether the motion vector predictor of the target block is to be derived depending on the specified condition.

For example, when the magnitude of the TMVP of the target block is equal to or greater than the first threshold, the processing unit may derive the motion vector predictor of the target block.

For example, when the magnitude of the TMVP of the target block is less than the first threshold, the processing unit may not derive the motion vector predictor of the target block.

In an embodiment, the magnitude of the TMVP may be calculated based on one or more of an x component and a y component of a motion vector of the TMVP.

For example, the magnitude of the TMVP may be the sum of the absolute value of the x component and the absolute value of the y component.

For example, the magnitude of the TMVP may be the sum of the square of the value of the x component and the square of the value of the y component.

For example, the magnitude of the TMVP may be the square root of the sum of the square of the value of the x component and the square of the value of the y component.

For example, the first threshold may be predefined by the encoding apparatus 1600 and the decoding apparatus 1700 according to the magnitude of an error depending on the magnitude of the TMVP. In other words, the first threshold may be a predefined constant.

For example, the first threshold may be set based on the coding parameter of the target block, the coding parameter of a block neighboring the target block, the coding parameter of a block in a col picture, and the coding parameter of a col block.

For example, the first threshold may be set for a specific unit. The set first threshold may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through a bitstream. When the first threshold is signaled, entropy encoding in the encoding apparatus 1600 and entropy decoding in the decoding apparatus 1700 may be used. The specific unit may be the above-described unit for encoding and/or decoding, such as an SPS, a PPS, a slice or a CTU.

If it is determined that the motion vector predictor of the target block is to be derived, step 2920 may be performed.

If it is determined that the motion vector predictor of the target block is not to be derived, the process may be terminated.

At step 2920, the processing unit may select a candidate block depending on a specified condition.

The processing unit may select a block that satisfies the specified condition from among all blocks in the col picture as the candidate block.

Alternatively, the processing unit may determine, for each of all blocks in the col picture, whether the corresponding block is to be selected as the candidate block depending on whether the corresponding block satisfies the specified condition.

In an embodiment, the processing unit may select the candidate block based on the location or area of a target block.

For example, the processing unit may select the candidate block based on at least one of the locations of the target block. The locations of the target block may be a center location, a top-left location, a top-right location, a bottom-left location, and a bottom-right location of the target block.

In an embodiment, the processing unit may select the candidate block based on a candidate area determined using the location or area of the target block.

In an embodiment, the processing unit may select the candidate block based on the location or area of a col block.

For example, the processing unit may select the candidate block based on at least one of the locations of the col block. The locations of the col block may be a center location, a top-left location, a top-right location, a bottom-left location, and a bottom-right location of the col block.

For example, the processing unit may select the candidate block based on a candidate area determined using the location or area of the col block.

For example, the processing unit may select only a block present in the candidate area, as the candidate block, from among blocks in the col picture.

For example, the candidate area may be a square area having a specific size in which the location of the col block is a center location. The horizontal length and the vertical length of the square may be determined depending on a second threshold. For example, the horizontal length and the vertical length of the square may be twice the second threshold.

For example, the processing unit may select a block in the col picture as the candidate block 1) when the absolute value of the difference between the x coordinate of the block in the col picture and the x coordinate of the target block is less than the second threshold, and 2) when the absolute value of the difference between the y coordinate of the block in the col picture and the y coordinate of the target block is less than the second threshold. In other words, blocks that are found as the candidate block so as to generate a motion vector predictor, among the blocks in the col picture, may be limited to blocks in a specific square. Here, the center of the specific square may be defined by the coordinates of the target block, and the horizontal length and the vertical length of the specific square may be twice the second threshold.

For example, the second threshold may be set based on the coding parameter of the target block, the coding parameter of a block neighboring the target block, the coding parameter of a block in a col picture, and the coding parameter of a col block. The second threshold may be set based on the size of the target block.

For example, the second threshold may be a predefined constant.

For example, the second threshold may be set for a specific unit. The set second threshold may be signaled from the encoding apparatus 1600 to the decoding apparatus 1700 through a bitstream. When the second threshold is signaled, entropy encoding in the encoding apparatus 1600 and entropy decoding in the decoding apparatus 1700 may be used. The specific unit may be the above-described unit for encoding and/or decoding, such as an SPS, a PPS, a slice or a CTU.

At step 2930, the processing unit may determine whether the motion information of the candidate block is to be used to generate the motion vector predictor of the target block.

Step 2930 may correspond to step 2510, described above with reference to FIG. 25. For example, step 2930 may include steps 2610, 2620, and 2630. Repetitive descriptions will be omitted here.

At step 2940, the processing unit may generate the motion vector predictor of the target block based on the motion information of the candidate block.

Step 2940 may correspond to step 2520, described above with reference to FIG. 25. For example, step 2940 may include steps 2710 and 2720. Repetitive descriptions will be omitted here.

Use of Motion Vector Predictor for Specific Inter-Prediction Mode

A UTMVP, generated through the above-described process, may be used in a merge mode, an AMVP mode, etc. as follows. Here, the UTMVP may be a motion vector predictor, described above with reference to FIGS. 23 to 29.

In the merge mode, the UTMVP may replace a TMVP. In other words, the above-described TMVP may not be used, and the description of the TMVP may be applied to the UTMVP.

In the merge mode, the TMVP may be used. In this case, the TMVP that is used may be a TMVP to which at least one of various embodiments of the above-described UTVMP is applied.

For example, in the merge mode, the UTMVP may selectively replace the TMVP. For example, when the magnitude of the TMVP is less than a threshold, the TMVP may be used, whereas when the magnitude of the TMVP is equal to or greater than the threshold, the UTMVP may be used.

Alternatively, the UTMVP in embodiments may be added to a merge candidate list, with higher priority than that of the TMVP. Here, the number of UTMVPs and the number of TMVPs may be individually predefined.

Alternatively, the UTMVP in embodiments may be added to a merge candidate list, with lower priority than that of the TMVP. Here, the number of UTMVPs and the number of TMVPs may be individually predefined.

In the merge mode, a PU may be partitioned into sub-blocks having a specific size, and a UTMVP may be calculated on each of the sub-blocks resulting from the partitioning, and the calculated UTMVPs may be used.

One or more of the above-described methods for the merge mode may be combined with each other. Further, the above-described methods for the merge mode may also be applied to a skip mode.

In an AMVP mode, a UTMVP may replace a TMVP. In other words, the above-described TMVP may not be used, and a description of the TMVP may be applied to the UTMVP.

In the AMVP mode, a TMVP may be used. At this time, the TMVP that is used may be a TMVP to which at least one of various embodiments of the above-described UTMVP is applied.

For example, in the AMVP mode, the UTMVP may selectively replace the TMVP. For example, when the magnitude of the TMVP is less than a threshold, the TMVP may be used, whereas when the magnitude of the TMVP is equal to or greater than the threshold, the UTMVP may be used.

Alternatively, the UTMVP in embodiments may be added to an AMVP candidate list, with higher priority than that of the TMVP. Here, the number of UTMVPs and the number of TMVPs may be individually predefined.

Alternatively, the UTMVP in embodiments may be added to an AMVP candidate list, with lower priority than that of the TMVP. Here, the number of UTMVPs and the number of TMVPs may be individually predefined.

One or more of the above-described methods for the AMVP mode may be combined with each other.

In the above-described embodiments, although the methods have been described based on flowcharts as a series of steps or units, the present disclosure is not limited to the sequence of the steps and some steps may be performed in a sequence different from that of the described steps or simultaneously with other steps. Further, those skilled in the art will understand that the steps shown in the flowchart are not exclusive and may further include other steps, or that one or more steps in the flowchart may be deleted without departing from the scope of the disclosure.

The above-described embodiments according to the present disclosure may be implemented as a program that can be executed by various computer means and may be recorded on a computer-readable storage medium. The computer-readable storage medium may include program instructions, data files, and data structures, either solely or in combination. Program instructions recorded on the storage medium may have been specially designed and configured for the present disclosure, or may be known to or available to those who have ordinary knowledge in the field of computer software.

The computer-readable storage medium may include information used in the embodiments of the present disclosure. For example, the computer-readable storage medium may include a bitstream, which may include information described in the embodiments of the present disclosure.

The computer-readable storage medium may include a non-transitory computer-readable medium.

Examples of the computer-readable storage medium include all types of hardware devices specially configured to record and execute program instructions, such as magnetic media, such as a hard disk, a floppy disk, and magnetic tape, optical media, such as compact disk (CD)-ROM and a digital versatile disk (DVD), magneto-optical media, such as a floptical disk, ROM, RAM, and flash memory. Examples of the program instructions include machine code, such as code created by a compiler, and high-level language code executable by a computer using an interpreter. The hardware devices may be configured to operate as one or more software modules in order to perform the operation of the present disclosure, and vice versa.

As described above, although the present disclosure has been described based on specific details such as detailed components and a limited number of embodiments and drawings, those are merely provided for easy understanding of the entire disclosure, the present disclosure is not limited to those embodiments, and those skilled in the art will practice various changes and modifications from the above description.

Accordingly, it should be noted that the spirit of the present disclose is not limited to the above-described embodiments, and the accompanying claims and equivalents and modifications thereof fall within the scope of the present disclosure. 

1. A decoding method comprising: determining a motion vector for a target block; and performing inter prediction for the target block using the motion vector.
 2. The decoding method of claim 1, wherein a motion vector predictor in a motion vector candidate list for the target block is used for determining the motion vector for the target block, and the motion vector predictor is generated based a plurality of motion vectors of a plurality of candidate blocks.
 3. The decoding method of claim 2, wherein the motion vector predictor is generated based on one or more available motion vectors of the plurality of the candidate blocks.
 4. The decoding method of claim 2, wherein the motion vector predictor is an average of the plurality of the motion vectors of the plurality of the candidate blocks.
 5. The decoding method of claim 2, wherein the number of the plurality of the candidate blocks is
 3. 6. The decoding method of claim 1, wherein a Sum of Absolute Differences (SAD) for each candidate block of the plurality of the candidate blocks is generated, and the motion vector of the target block is determined based on SADs for the plurality of the candidate blocks.
 7. The decoding method of claim 6, wherein the motion vector is determined based on a minimum SAD among the SADs.
 8. The decoding method of claim 6, wherein the SADs are computed based on reconstructed blocks.
 9. The decoding method of claim 6, wherein the plurality of the candidate blocks are block in a candidate area determined based on a location of the target block.
 10. The decoding method of claim 1, wherein a plurality of motion vectors for a plurality of blocks are determined based on the target block, and the inter prediction for the target block is performed based on the plurality of the motion vectors.
 11. The decoding method of claim 10, wherein the plurality of the motion vectors are determined based on a col block of the target block.
 12. The decoding method of claim 10, wherein the plurality of the motion vectors are determined based on a reference picture index, and the reference picture is specified based on the target block.
 13. The decoding method of claim 10, wherein the plurality of the motion vectors are determined based on whether a picture indicated based on the target block is a specific reference picture or not.
 14. The decoding method of claim 10, wherein the target block is partitioned into a plurality of sub-blocks, and motion vector predictors of the plurality of the sub-blocks are used for the inter prediction.
 15. The decoding method of claim 14, wherein the inter prediction is performed based on reference picture indexes of the plurality of the sub-blocks.
 16. The decoding method of claim 14, wherein a motion vector predictor of a sub-block of the plurality of the sub-blocks is determined based on whether a reference picture index of the sub-block indicates a specific reference picture or not.
 17. The decoding method of claim 14, wherein the motion vector predictors of the plurality of the sub-blocks are determined based on a Picture Order Count (POC) of a target picture comprising the target block.
 18. The decoding method of claim 1, wherein the motion vector is determined based on a size of the target block.
 19. An encoding method comprising: determining a motion vector for a target block; and performing inter prediction for the target block using the motion vector.
 20. A non-transitory computer-readable medium storing a bitstream, the bitstream comprising: inter prediction information for a target block, wherein a motion vector for the target block is determined based on the inter prediction information, and inter prediction for the target block is performed using the motion vector. 